diff --git a/cli/src/main/java/hudson/cli/FullDuplexHttpStream.java b/cli/src/main/java/hudson/cli/FullDuplexHttpStream.java
index f7f73e69ae..27e8a618b2 100644
--- a/cli/src/main/java/hudson/cli/FullDuplexHttpStream.java
+++ b/cli/src/main/java/hudson/cli/FullDuplexHttpStream.java
@@ -1,11 +1,17 @@
 package hudson.cli;
 
+import java.io.BufferedReader;
 import java.io.IOException;
 import java.io.InputStream;
+import java.io.InputStreamReader;
 import java.io.OutputStream;
+import java.io.OutputStreamWriter;
+import java.io.Reader;
 import java.net.HttpURLConnection;
 import java.net.URL;
 import java.util.UUID;
+import java.util.logging.Level;
+import java.util.logging.Logger;
 
 /**
  * Creates a capacity-unlimited bi-directional {@link InputStream}/{@link OutputStream} pair over
@@ -34,12 +40,17 @@ public class FullDuplexHttpStream {
     public FullDuplexHttpStream(URL target) throws IOException {
         this.target = target;
 
+        CrumbData crumbData = new CrumbData();
+        
         // server->client
         HttpURLConnection con = (HttpURLConnection) target.openConnection();
         con.setDoOutput(true); // request POST to avoid caching
         con.setRequestMethod("POST");
         con.addRequestProperty("Session",uuid.toString());
         con.addRequestProperty("Side","download");
+        if(crumbData.isValid) {
+            con.addRequestProperty(crumbData.crumbName, crumbData.crumb);
+        }
         con.getOutputStream().close();
         input = con.getInputStream();
         // make sure we hit the right URL
@@ -53,8 +64,54 @@ public class FullDuplexHttpStream {
         con.setChunkedStreamingMode(0);
         con.addRequestProperty("Session",uuid.toString());
         con.addRequestProperty("Side","upload");
+        if(crumbData.isValid) {
+            con.addRequestProperty(crumbData.crumbName, crumbData.crumb);
+        }
         output = con.getOutputStream();
     }
 
     static final int BLOCK_SIZE = 1024;
+    static final Logger LOGGER = Logger.getLogger(FullDuplexHttpStream.class.getName());
+    
+    private final class CrumbData {
+    	String crumbName;
+    	String crumb;
+    	boolean isValid;
+
+    	private CrumbData() {
+            this.crumbName = "";
+            this.crumb = "";
+            this.isValid = false;
+            getData();
+    	}
+
+    	private void getData() {
+            try {
+                String base = createCrumbUrlBase();
+                crumbName = readData(base+"?xpath=/*/crumbRequestField/text()");
+                crumb = readData(base+"?xpath=/*/crumb/text()");
+                isValid = true;
+                LOGGER.fine("Crumb data: "+crumbName+"="+crumb);
+            }
+            catch (IOException e) {
+                LOGGER.log(Level.WARNING,"Failed to get crumb data",e);
+            }
+    	}
+
+    	private String createCrumbUrlBase() {
+            String url = target.toExternalForm();    		
+            return new StringBuilder(url.substring(0, url.lastIndexOf("/cli"))).append("/crumbIssuer/api/xml/").toString();
+    	}
+
+    	private String readData(String dest) throws IOException {
+            HttpURLConnection con = (HttpURLConnection) new URL(dest).openConnection();
+            try {
+                BufferedReader reader = new BufferedReader(new InputStreamReader(con.getInputStream()));
+                return reader.readLine();
+            }
+            finally {
+                con.disconnect();
+            }
+        }
+    }
 }
diff --git a/core/pom.xml b/core/pom.xml
index ceb73d4166..cc95dee338 100644
--- a/core/pom.xml
+++ b/core/pom.xml
@@ -702,6 +702,17 @@ THE SOFTWARE.
       <artifactId>jinterop-wmi</artifactId>
       <version>1.0</version>
     </dependency>
+    <dependency>
+      <groupId>org.jvnet.hudson</groupId>
+      <artifactId>htmlunit</artifactId>
+      <version>2.2-hudson-9</version>
+      <exclusions>
+        <exclusion>
+          <groupId>xalan</groupId>
+          <artifactId>xalan</artifactId>
+        </exclusion>
+      </exclusions>
+    </dependency>
 
     <!-- offline profiler API to put in the classpath if we need it -->
     <!--dependency>
diff --git a/core/src/main/java/hudson/Functions.java b/core/src/main/java/hudson/Functions.java
index f21ef02ea2..a34afa183a 100644
--- a/core/src/main/java/hudson/Functions.java
+++ b/core/src/main/java/hudson/Functions.java
@@ -47,6 +47,7 @@ import hudson.security.AccessControlled;
 import hudson.security.AuthorizationStrategy;
 import hudson.security.Permission;
 import hudson.security.SecurityRealm;
+import hudson.security.csrf.CrumbIssuer;
 import hudson.slaves.Cloud;
 import hudson.slaves.ComputerLauncher;
 import hudson.slaves.NodeProperty;
@@ -1132,6 +1133,56 @@ public class Functions {
         return body;
     }
 
+    public static List<Descriptor<CrumbIssuer>> getCrumbIssuerDescriptors() {
+        return CrumbIssuer.all();
+    }
+    
+    public static String getCrumb(StaplerRequest req) {
+        CrumbIssuer issuer = Hudson.getInstance().getCrumbIssuer();
+        if (issuer != null) {
+            return issuer.getCrumb(req);
+        }
+        
+        return "";
+    }
+    
+    public static String getCrumbRequestField() {
+        CrumbIssuer issuer = Hudson.getInstance().getCrumbIssuer();
+        if (issuer != null) {
+            return issuer.getDescriptor().getCrumbRequestField();
+        }
+        
+        return "";
+    }
+    
+    public static String getCrumbAsJSONParameterBlock(StaplerRequest req) {
+        StringBuilder builder = new StringBuilder();
+        if (Hudson.getInstance().isUseCrumbs()) {
+            builder.append("parameters:{\"");
+            builder.append(getCrumbRequestField());
+            builder.append("\":\"");
+            builder.append(getCrumb(req));
+            builder.append("\"}");
+        }
+        return builder.toString();
+    }
+    
+    public static String getReplaceDescriptionInvoker(StaplerRequest req) {
+    	StringBuilder builder = new StringBuilder();
+    	if (isAutoRefresh(req)) {
+    		builder.append("null");
+    	} else {
+    		builder.append("'return replaceDescription(");
+    		builder.append("\\'");
+    		builder.append(getCrumbRequestField());
+    		builder.append("\\',\\'");
+    		builder.append(getCrumb(req));
+    		builder.append("\\'");
+    		builder.append(");'");
+    	}
+    	return builder.toString();
+    }
+    
     private static final Pattern SCHEME = Pattern.compile("[a-z]+://.+");
 
     /**
diff --git a/core/src/main/java/hudson/model/DownloadService.java b/core/src/main/java/hudson/model/DownloadService.java
index e9a84933b4..8befdb0e77 100644
--- a/core/src/main/java/hudson/model/DownloadService.java
+++ b/core/src/main/java/hudson/model/DownloadService.java
@@ -3,6 +3,7 @@ package hudson.model;
 import hudson.Extension;
 import hudson.ExtensionList;
 import hudson.ExtensionPoint;
+import hudson.security.csrf.CrumbIssuer;
 import hudson.util.QuotedStringTokenizer;
 import hudson.util.TextFile;
 import hudson.util.TimeUnit2;
@@ -38,9 +39,22 @@ public class DownloadService extends PageDecorator {
         StringBuilder buf = new StringBuilder();
         if(Hudson.getInstance().hasPermission(Hudson.READ)) {
             long now = System.currentTimeMillis();
+            CrumbIssuer ci = Hudson.getInstance().getCrumbIssuer();
+            String crumbName = null;
+            String crumb = null;
+            if(ci!=null) {
+                crumbName = ci.getCrumbRequestField();
+                crumb = ci.getCrumb();
+            }
             for (Downloadable d : Downloadable.all()) {
                 if(d.getDue()<now) {
-                     buf.append("<script>downloadService.download(")
+                    buf.append("<script>");
+                    if(ci!=null) {
+                        buf.append("downloadService.crumbName="+QuotedStringTokenizer.quote(crumbName))
+                           .append(";downloadService.crumb="+QuotedStringTokenizer.quote(crumb))
+                           .append(';');
+                    }
+                    buf.append("downloadService.download(")
                        .append(QuotedStringTokenizer.quote(d.getId()))
                        .append(',')
                        .append(QuotedStringTokenizer.quote(d.getUrl()))
@@ -197,3 +211,4 @@ public class DownloadService extends PageDecorator {
         private static final Logger LOGGER = Logger.getLogger(Downloadable.class.getName());
     }
 }
+
diff --git a/core/src/main/java/hudson/model/Hudson.java b/core/src/main/java/hudson/model/Hudson.java
index e126a00d54..1b734297e3 100644
--- a/core/src/main/java/hudson/model/Hudson.java
+++ b/core/src/main/java/hudson/model/Hudson.java
@@ -1,7 +1,7 @@
 /*
  * The MIT License
  * 
- * Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Erik Ramfelt, Koichi Fujikawa, Red Hat, Inc., Seiji Sogabe, Stephen Connolly, Tom Huybrechts
+ * Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Erik Ramfelt, Koichi Fujikawa, Red Hat, Inc., Seiji Sogabe, Stephen Connolly, Tom Huybrechts, Yahoo! Inc.
  * 
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -79,6 +79,9 @@ import hudson.security.Permission;
 import hudson.security.PermissionGroup;
 import hudson.security.SecurityMode;
 import hudson.security.SecurityRealm;
+import hudson.security.csrf.CrumbFilter;
+import hudson.security.csrf.CrumbIssuer;
+import hudson.security.csrf.CrumbIssuerDescriptor;
 import hudson.slaves.ComputerListener;
 import hudson.slaves.NodeProperty;
 import hudson.slaves.NodePropertyDescriptor;
@@ -416,6 +419,13 @@ public final class Hudson extends Node implements ItemGroup<TopLevelItem>, Stapl
      */
     private String label="";
 
+    private Boolean useCrumbs;
+    
+    /**
+     * {@link hudson.security.csrf.CrumbIssuer}
+     */
+    private volatile CrumbIssuer crumbIssuer;
+    
     /**
      * All labels known to Hudson. This allows us to reuse the same label instances
      * as much as possible, even though that's not a strict requirement.
@@ -1582,6 +1592,10 @@ public final class Hudson extends Node implements ItemGroup<TopLevelItem>, Stapl
         return securityRealm!=SecurityRealm.NO_AUTHENTICATION || authorizationStrategy!=AuthorizationStrategy.UNSECURED;
     }
 
+    public boolean isUseCrumbs() {
+        return (useCrumbs != null) && useCrumbs;
+    }
+    
     /**
      * Returns the constant that captures the three basic security modes
      * in Hudson.
@@ -2047,6 +2061,9 @@ public final class Hudson extends Node implements ItemGroup<TopLevelItem>, Stapl
             setSecurityRealm(SecurityRealm.NO_AUTHENTICATION);
         }
 
+        // Initialize the filter with the crumb issuer
+        setCrumbIssuer(crumbIssuer);
+        
         LOGGER.info(String.format("Took %s ms to load",System.currentTimeMillis()-startTime));
         if(KILL_AFTER_LOAD)
             System.exit(0);
@@ -2149,6 +2166,15 @@ public final class Hudson extends Node implements ItemGroup<TopLevelItem>, Stapl
                 authorizationStrategy = AuthorizationStrategy.UNSECURED;
             }
 
+            if (json.has("csrf")) {
+            	useCrumbs = true;
+            	JSONObject csrf = json.getJSONObject("csrf");
+            	setCrumbIssuer(CrumbIssuer.all().newInstanceFromRadioList(csrf, "issuer"));
+            } else {
+            	useCrumbs = null;
+            	setCrumbIssuer(null);
+            }
+            
             noUsageStatistics = json.has("usageStatisticsCollected") ? null : true;
 
             {
@@ -2219,6 +2245,9 @@ public final class Hudson extends Node implements ItemGroup<TopLevelItem>, Stapl
             for( PageDecorator d : PageDecorator.all() )
                 result &= configureDescriptor(req,json,d);
 
+            for( Descriptor<CrumbIssuer> d : CrumbIssuer.all() )
+                result &= configureDescriptor(req,json, d);
+            
             for( ToolDescriptor d : ToolInstallation.all() )
                 result &= configureDescriptor(req,json,d);
 
@@ -2247,6 +2276,19 @@ public final class Hudson extends Node implements ItemGroup<TopLevelItem>, Stapl
         }
     }
 
+    public CrumbIssuer getCrumbIssuer() {
+        return crumbIssuer;
+    }
+    
+    public void setCrumbIssuer(CrumbIssuer issuer) {
+        crumbIssuer = issuer;
+        CrumbFilter.get(servletContext).setCrumbIssuer(issuer);
+    }
+
+    public void setUseCrumbs(Boolean use) {
+        useCrumbs = use;
+    }
+    
     public synchronized void doTestPost( StaplerRequest req, StaplerResponse rsp ) throws IOException, ServletException {
         JSONObject form = req.getSubmittedForm();
         rsp.sendRedirect("foo");
@@ -2608,6 +2650,9 @@ public final class Hudson extends Node implements ItemGroup<TopLevelItem>, Stapl
     public void doDoFingerprintCheck( StaplerRequest req, StaplerResponse rsp ) throws IOException, ServletException {
         // Parse the request
         MultipartFormDataParser p = new MultipartFormDataParser(req);
+        if(Hudson.getInstance().isUseCrumbs() && !Hudson.getInstance().getCrumbIssuer().validateCrumb(req, p)) {
+            rsp.sendError(HttpServletResponse.SC_FORBIDDEN,"No crumb found");                
+        }
         try {
             rsp.sendRedirect2(req.getContextPath()+"/fingerprint/"+
                 Util.getDigestOf(p.getFileItem("name").getInputStream())+'/');
diff --git a/core/src/main/java/hudson/scm/SubversionSCM.java b/core/src/main/java/hudson/scm/SubversionSCM.java
index 073272e593..8c73f51714 100644
--- a/core/src/main/java/hudson/scm/SubversionSCM.java
+++ b/core/src/main/java/hudson/scm/SubversionSCM.java
@@ -96,6 +96,7 @@ import org.tmatesoft.svn.core.wc.SVNWCUtil;
 import org.tmatesoft.svn.core.wc.SVNLogClient;
 
 import javax.servlet.ServletException;
+import javax.servlet.http.HttpServletResponse;
 import javax.xml.transform.stream.StreamResult;
 import java.io.BufferedOutputStream;
 import java.io.BufferedReader;
@@ -1286,6 +1287,10 @@ public class SubversionSCM extends SCM implements Serializable {
 
             MultipartFormDataParser parser = new MultipartFormDataParser(req);
 
+            if(Hudson.getInstance().isUseCrumbs() && !Hudson.getInstance().getCrumbIssuer().validateCrumb(req, parser)) {
+                rsp.sendError(HttpServletResponse.SC_FORBIDDEN,"No crumb found");                
+            }
+            
             String url = parser.get("url");
 
             String kind = parser.get("kind");
diff --git a/core/src/main/java/hudson/security/csrf/CrumbFilter.java b/core/src/main/java/hudson/security/csrf/CrumbFilter.java
new file mode 100644
index 0000000000..29ad7127c0
--- /dev/null
+++ b/core/src/main/java/hudson/security/csrf/CrumbFilter.java
@@ -0,0 +1,133 @@
+/**
+ * Copyright (c) 2008-2009 Yahoo! Inc. 
+ * All rights reserved. 
+ * The copyrights to the contents of this file are licensed under the MIT License (http://www.opensource.org/licenses/mit-license.php)
+ */
+package hudson.security.csrf;
+
+import java.io.IOException;
+import java.util.Enumeration;
+import java.util.logging.Logger;
+
+import javax.servlet.Filter;
+import javax.servlet.FilterChain;
+import javax.servlet.FilterConfig;
+import javax.servlet.ServletContext;
+import javax.servlet.ServletException;
+import javax.servlet.ServletRequest;
+import javax.servlet.ServletResponse;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+/**
+ * Checks for and validates crumbs on requests that cause state changes, to
+ * protect against cross site request forgeries.
+ * 
+ * @author dty
+ *
+ */
+public class CrumbFilter implements Filter {
+
+    private volatile CrumbIssuer crumbIssuer;
+
+    public CrumbIssuer getCrumbIssuer() {
+        return crumbIssuer;
+    }
+
+    public void setCrumbIssuer(CrumbIssuer issuer) {
+        crumbIssuer = issuer;
+    }
+
+    /**
+     * Gets the {@link CrumbFilter} created for the given {@link ServletContext}.
+     */
+    public static CrumbFilter get(ServletContext context) {
+        return (CrumbFilter) context.getAttribute(CrumbFilter.class.getName());
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public void init(FilterConfig filterConfig) throws ServletException {
+        // this is how we make us available to the rest of Hudson.
+        filterConfig.getServletContext().setAttribute(CrumbFilter.class.getName(), this);
+    }
+
+    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
+        if (crumbIssuer == null) {
+            chain.doFilter(request, response);
+            return;
+        }
+        if (!(request instanceof HttpServletRequest)) {
+            chain.doFilter(request, response);
+            return;
+        }
+
+        HttpServletRequest httpRequest = (HttpServletRequest) request;
+        String crumbFieldName = crumbIssuer.getDescriptor().getCrumbRequestField();
+        String crumbSalt = crumbIssuer.getDescriptor().getCrumbSalt();
+
+        if ("POST".equals(httpRequest.getMethod())) {
+            String crumb = httpRequest.getHeader(crumbFieldName);
+            boolean valid = false;
+            if (crumb == null) {
+                Enumeration<?> paramNames = request.getParameterNames();
+                while (paramNames.hasMoreElements()) {
+                    String paramName = (String) paramNames.nextElement();
+                    if (crumbFieldName.equals(paramName)) {
+                        crumb = request.getParameter(paramName);
+                        break;
+                    }
+                }
+            }
+            if (crumb != null) {
+                if (crumbIssuer.validateCrumb(httpRequest, crumbSalt, crumb)) {
+                    valid = true;
+                } else {
+                    LOGGER.warning("Found invalid crumb " + crumb +
+                            ".  Will check remaining parameters for a valid one...");
+                }
+            }
+            // Multipart requests need to be handled by each handler.
+            if (valid || isMultipart(httpRequest)) {
+                chain.doFilter(request, response);
+            } else {
+                LOGGER.warning("No valid crumb was included in request for " + httpRequest.getRequestURI() + ".  Returning " + HttpServletResponse.SC_FORBIDDEN + ".");
+                ((HttpServletResponse) response).sendError(HttpServletResponse.SC_FORBIDDEN);
+            }
+        } else {
+            chain.doFilter(request, response);
+        }
+    }
+
+    protected static boolean isMultipart(HttpServletRequest request) {
+        if (request == null) {
+            return false;
+        }
+
+        String contentType = request.getContentType();
+        if (contentType == null) {
+            return false;
+        }
+
+        String[] parts = contentType.split(";");
+        if (parts.length == 0) {
+            return false;
+        }
+
+        for (int i = 0; i < parts.length; i++) {
+            if ("multipart/form-data".equals(parts[i])) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public void destroy() {
+    }
+    private static final Logger LOGGER = Logger.getLogger(CrumbFilter.class.getName());
+}
diff --git a/core/src/main/java/hudson/security/csrf/CrumbIssuer.java b/core/src/main/java/hudson/security/csrf/CrumbIssuer.java
new file mode 100644
index 0000000000..17d5a0b9f0
--- /dev/null
+++ b/core/src/main/java/hudson/security/csrf/CrumbIssuer.java
@@ -0,0 +1,155 @@
+/**
+ * Copyright (c) 2008-2009 Yahoo! Inc.
+ * All rights reserved.
+ * The copyrights to the contents of this file are licensed under the MIT License (http://www.opensource.org/licenses/mit-license.php)
+ */
+package hudson.security.csrf;
+
+import javax.servlet.ServletRequest;
+
+import org.kohsuke.stapler.Stapler;
+import org.kohsuke.stapler.export.Exported;
+import org.kohsuke.stapler.export.ExportedBean;
+
+import hudson.DescriptorExtensionList;
+import hudson.ExtensionPoint;
+import hudson.model.Api;
+import hudson.model.Describable;
+import hudson.model.Descriptor;
+import hudson.model.Hudson;
+import hudson.util.MultipartFormDataParser;
+
+/**
+ * A CrumbIssuer represents an algorithm to generate a nonce value, known as a
+ * crumb, to counter cross site request forgery exploits. Crumbs are typically
+ * hashes incorporating information that uniquely identifies an agent that sends
+ * a request, along with a guarded secret so that the crumb value cannot be
+ * forged by a third party.
+ *
+ * @author dty
+ * @see http://en.wikipedia.org/wiki/XSRF
+ */
+@ExportedBean
+public abstract class CrumbIssuer implements Describable<CrumbIssuer>, ExtensionPoint {
+
+    private static final String CRUMB_ATTRIBUTE = CrumbIssuer.class.getName() + "_crumb";
+
+    /**
+     * Get the name of the request parameter the crumb will be stored in. Exposed
+     * here for the remote API.
+     */
+    @Exported
+    public String getCrumbRequestField() {
+        return getDescriptor().getCrumbRequestField();
+    }
+
+    /**
+     * Get a crumb value based on user specific information in the current request.
+     * Intended for use only by the remote API.
+     * @return
+     */
+    @Exported
+    public String getCrumb() {
+        return getCrumb(Stapler.getCurrentRequest());
+    }
+
+    /**
+     * Get a crumb value based on user specific information in the request.
+     * @param request
+     * @return
+     */
+    public String getCrumb(ServletRequest request) {
+        String crumb = null;
+        if (request != null) {
+            crumb = (String) request.getAttribute(CRUMB_ATTRIBUTE);
+        }
+        if (crumb == null) {
+            crumb = issueCrumb(request, getDescriptor().getCrumbSalt());
+            if (request != null) {
+                if ((crumb != null) && !crumb.isEmpty()) {
+                    request.setAttribute(CRUMB_ATTRIBUTE, crumb);
+                } else {
+                    request.removeAttribute(CRUMB_ATTRIBUTE);
+                }
+            }
+        }
+
+        return crumb;
+    }
+
+    /**
+     * Create a crumb value based on user specific information in the request.
+     * The crumb should be generated by building a cryptographic hash of:
+     * <ul>
+     *  <li>relevant information in the request that can uniquely identify the client
+     *  <li>the salt value
+     *  <li>an implementation specific guarded secret.
+     * </ul>
+     *
+     * @param request
+     * @param salt
+     * @return
+     */
+    protected abstract String issueCrumb(ServletRequest request, String salt);
+
+    /**
+     * Get a crumb from a request parameter and validate it against other data
+     * in the current request. The salt and request parameter that is used is
+     * defined by the current configuration.
+     *
+     * @param request
+     * @return
+     */
+    public boolean validateCrumb(ServletRequest request) {
+        CrumbIssuerDescriptor<CrumbIssuer> desc = getDescriptor();
+        String crumbField = desc.getCrumbRequestField();
+        String crumbSalt = desc.getCrumbSalt();
+
+        return validateCrumb(request, crumbSalt, request.getParameter(crumbField));
+    }
+
+    /**
+     * Get a crumb from multipart form data and validate it against other data
+     * in the current request. The salt and request parameter that is used is
+     * defined by the current configuration.
+     *
+     * @param request
+     * @param parser
+     * @return
+     */
+    public boolean validateCrumb(ServletRequest request, MultipartFormDataParser parser) {
+        CrumbIssuerDescriptor<CrumbIssuer> desc = getDescriptor();
+        String crumbField = desc.getCrumbRequestField();
+        String crumbSalt = desc.getCrumbSalt();
+
+        return validateCrumb(request, crumbSalt, parser.get(crumbField));
+    }
+
+    /**
+     * Validate a previously created crumb against information in the current request.
+     *
+     * @param request
+     * @param salt
+     * @param crumb The previously generated crumb to validate against information in the current request
+     * @return
+     */
+    public abstract boolean validateCrumb(ServletRequest request, String salt, String crumb);
+
+    /**
+     * Access global configuration for the crumb issuer.
+     */
+    public CrumbIssuerDescriptor<CrumbIssuer> getDescriptor() {
+        return (CrumbIssuerDescriptor<CrumbIssuer>) Hudson.getInstance().getDescriptor(getClass());
+    }
+
+    /**
+     * Returns all the registered {@link CrumbIssuer} descriptors.
+     */
+    public static DescriptorExtensionList<CrumbIssuer, Descriptor<CrumbIssuer>> all() {
+        return Hudson.getInstance().getDescriptorList(CrumbIssuer.class);
+    }
+
+    public Api getApi() {
+        return new Api(this);
+    }
+}
diff --git a/core/src/main/java/hudson/security/csrf/CrumbIssuerDescriptor.java b/core/src/main/java/hudson/security/csrf/CrumbIssuerDescriptor.java
new file mode 100644
index 0000000000..ba712a049d
--- /dev/null
+++ b/core/src/main/java/hudson/security/csrf/CrumbIssuerDescriptor.java
@@ -0,0 +1,117 @@
+/**
+ * Copyright (c) 2008-2009 Yahoo! Inc. 
+ * All rights reserved. 
+ * The copyrights to the contents of this file are licensed under the MIT License (http://www.opensource.org/licenses/mit-license.php)
+ */
+package hudson.security.csrf;
+
+import org.kohsuke.stapler.StaplerRequest;
+
+import hudson.Util;
+import hudson.model.Descriptor;
+
+/**
+ * Describes global configuration for crumb issuers. Create subclasses to specify
+ * additional global configuration for custom crumb issuers.
+ * 
+ * @author dty
+ *
+ */
+public abstract class CrumbIssuerDescriptor<T extends CrumbIssuer> extends Descriptor<CrumbIssuer> {
+
+    private String crumbSalt;
+    private String crumbRequestField;
+
+    /**
+     * Crumb issuers always take a salt and a request field name.
+     *
+     * @param salt Salt value
+     * @param crumbRequestField Request parameter name containing crumb from previous response
+     */
+    protected CrumbIssuerDescriptor(String salt, String crumbRequestField) {
+        setCrumbSalt(salt);
+        setCrumbRequestField(crumbRequestField);
+    }
+
+    /**
+     * Get the salt value.
+     * @return
+     */
+    public String getCrumbSalt() {
+        return crumbSalt;
+    }
+
+    /**
+     * Set the salt value. Must not be null.
+     * @param salt
+     */
+    public void setCrumbSalt(String salt) {
+        if (Util.fixEmptyAndTrim(salt) == null) {
+            crumbSalt = "hudson.crumb";
+        } else {
+            crumbSalt = salt;
+        }
+    }
+
+    /**
+     * Gets the request parameter name that contains the crumb generated from a
+     * previous response.
+     *
+     * @return
+     */
+    public String getCrumbRequestField() {
+        return crumbRequestField;
+    }
+
+    /**
+     * Set the request parameter name. Must not be null.
+     *
+     * @param requestField
+     */
+    public void setCrumbRequestField(String requestField) {
+        if (Util.fixEmptyAndTrim(requestField) == null) {
+            crumbRequestField = ".crumb";
+        } else {
+            crumbRequestField = requestField;
+        }
+    }
+
+    @Override
+    public boolean configure(StaplerRequest request) {
+        setCrumbSalt(request.getParameter("csrf_crumbSalt"));
+        setCrumbRequestField(request.getParameter("csrf_crumbRequestField"));
+        save();
+
+        return true;
+    }
+
+    /**
+     * Returns the Jelly script that contains common configuration.
+     */
+    @Override
+    public final String getConfigPage() {
+        return getViewPage(CrumbIssuer.class, "config.jelly");
+    }
+
+    /**
+     * Returns a subclass specific configuration page. The base CrumbIssuerDescriptor
+     * class provides configuration options that are common to all crumb issuers.
+     * Implementations may provide additional configuration options which are
+     * kept in Jelly script file tied to the subclass.
+     * <p>
+     * By default, an empty string is returned, which signifies no additional
+     * configuration is needed for a crumb issuer. Override this method if your
+     * crumb issuer has additional configuration options.
+     * <p>
+     * A typical implementation of this method would look like:
+     * <p>
+     * <code>
+     * return getViewPage(clazz, "config.jelly");
+     * </code>
+     *
+     * @return An empty string, signifying no additional configuration.
+     */
+    public String getSubConfigPage() {
+        return "";
+    }
+}
diff --git a/core/src/main/java/hudson/security/csrf/DefaultCrumbIssuer.java b/core/src/main/java/hudson/security/csrf/DefaultCrumbIssuer.java
new file mode 100644
index 0000000000..d2e635d8e1
--- /dev/null
+++ b/core/src/main/java/hudson/security/csrf/DefaultCrumbIssuer.java
@@ -0,0 +1,111 @@
+/**
+ * Copyright (c) 2008-2009 Yahoo! Inc. 
+ * All rights reserved. 
+ * The copyrights to the contents of this file are licensed under the MIT License (http://www.opensource.org/licenses/mit-license.php)
+ */
+package hudson.security.csrf;
+
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+import hudson.Extension;
+import hudson.model.Hudson;
+import hudson.model.ModelObject;
+
+import javax.servlet.ServletRequest;
+import javax.servlet.http.HttpServletRequest;
+
+import net.sf.json.JSONObject;
+
+import org.acegisecurity.Authentication;
+import org.kohsuke.stapler.StaplerRequest;
+
+/**
+ * A crumb issuing algorithm based on the request principal and the remote address.
+ * 
+ * @author dty
+ *
+ */
+public class DefaultCrumbIssuer extends CrumbIssuer {
+
+    private MessageDigest md;
+
+    DefaultCrumbIssuer() {
+        try {
+            this.md = MessageDigest.getInstance("MD5");
+        } catch (NoSuchAlgorithmException e) {
+            this.md = null;
+            LOGGER.log(Level.SEVERE, "Can't find MD5", e);
+        }
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    protected String issueCrumb(ServletRequest request, String salt) {
+        if (request instanceof HttpServletRequest) {
+            if (md != null) {
+                HttpServletRequest req = (HttpServletRequest) request;
+                StringBuilder buffer = new StringBuilder();
+                Authentication a = Hudson.getAuthentication();
+                if (a != null) {
+                    buffer.append(a.getName());
+                }
+                buffer.append(';');
+                buffer.append(req.getRemoteAddr());
+
+                md.update(buffer.toString().getBytes());
+                md.update(salt.getBytes());
+                byte[] crumbBytes = md.digest(Hudson.getInstance().getSecretKey().getBytes());
+
+                StringBuilder hexString = new StringBuilder();
+                for (int i = 0; i < crumbBytes.length; i++) {
+                    String hex = Integer.toHexString(0xFF & crumbBytes[i]);
+                    if (hex.length() == 1) {
+                        hexString.append('0');
+                    }
+                    hexString.append(hex);
+                }
+                return hexString.toString();
+            }
+        }
+        return null;
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public boolean validateCrumb(ServletRequest request, String salt, String crumb) {
+        if (request instanceof HttpServletRequest) {
+            String newCrumb = issueCrumb(request, salt);
+            if ((newCrumb != null) && (crumb != null)) {
+                return newCrumb.equals(crumb);
+            }
+        }
+        return false;
+    }
+
+    @Extension
+    public static final class DescriptorImpl extends CrumbIssuerDescriptor<DefaultCrumbIssuer> implements ModelObject {
+
+        public DescriptorImpl() {
+            super(null, null);
+            load();
+        }
+
+        @Override
+        public String getDisplayName() {
+            return "Default Crumb Issuer";
+        }
+
+        public DefaultCrumbIssuer newInstance(StaplerRequest req, JSONObject formData) throws FormException {
+            return new DefaultCrumbIssuer();
+        }
+    }
+    
+    private static final Logger LOGGER = Logger.getLogger(DefaultCrumbIssuer.class.getName());
+}
diff --git a/core/src/main/resources/hudson/PluginManager/installed.jelly b/core/src/main/resources/hudson/PluginManager/installed.jelly
index 33c8a321af..2ce3ff8761 100644
--- a/core/src/main/resources/hudson/PluginManager/installed.jelly
+++ b/core/src/main/resources/hudson/PluginManager/installed.jelly
@@ -1,7 +1,7 @@
 <!--
 The MIT License
 
-Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Seiji Sogabe
+Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Seiji Sogabe, Yahoo! Inc.
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -110,6 +110,9 @@ THE SOFTWARE.
 
           <!-- trigger -->
           new Ajax.Request(btn.getAttribute('url')+"/make"+(btn.checked?"Enable":"Disable")+"d", {
+            <j:if test="${app.useCrumbs}">
+            parameters : { "${h.getCrumbRequestField()}": "${h.getCrumb(request)}" },
+            </j:if>
             onFailure : function(req,o) {
               $('needRestart').innerHTML = req.responseText;
             }
diff --git a/core/src/main/resources/hudson/model/AbstractProject/sidepanel.jelly b/core/src/main/resources/hudson/model/AbstractProject/sidepanel.jelly
index 9aa3fd4288..f69a46e461 100644
--- a/core/src/main/resources/hudson/model/AbstractProject/sidepanel.jelly
+++ b/core/src/main/resources/hudson/model/AbstractProject/sidepanel.jelly
@@ -1,7 +1,7 @@
 <!--
 The MIT License
 
-Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Erik Ramfelt, Tom Huybrechts, id:cactusman
+Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Erik Ramfelt, Tom Huybrechts, id:cactusman, Yahoo! Inc.
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -46,7 +46,8 @@ THE SOFTWARE.
                   onclick="${it.parameterized?null:'return build(this)'}" permission="${it.BUILD}" />
           <script>
             function build(a) {
-              new Ajax.Request(a.href,{method:"post"});
+              new Ajax.Request(a.href,{method:"post",${h.getCrumbAsJSONParameterBlock(request)} });
+              
               hoverNotification('${%Build scheduled}',a.parentNode);
               return false;
             }
diff --git a/core/src/main/resources/hudson/model/Hudson/configure.jelly b/core/src/main/resources/hudson/model/Hudson/configure.jelly
index f326fee104..681e5e72f3 100644
--- a/core/src/main/resources/hudson/model/Hudson/configure.jelly
+++ b/core/src/main/resources/hudson/model/Hudson/configure.jelly
@@ -1,7 +1,7 @@
 <!--
 The MIT License
 
-Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Erik Ramfelt, Jean-Baptiste Quenot, Stephen Connolly, Tom Huybrechts
+Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Erik Ramfelt, Jean-Baptiste Quenot, Stephen Connolly, Tom Huybrechts, Yahoo! Inc.
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -88,6 +88,19 @@ THE SOFTWARE.
         </f:entry>
       </f:optionalBlock>
 
+      <j:if test="${!empty(h.crumbIssuerDescriptors)}">
+	    <f:optionalBlock name="csrf" title="${%Prevent Cross Site Request Forgery exploits}"
+	                     checked="${it.useCrumbs}" help="/help/system-config/csrf.html">
+	      <f:entry title="${Crumbs}">
+	        <table style="width:100%">
+	          <f:descriptorRadioList title="${%Crumb Algorithm}" varName="issuer"
+	                                 instance="${it.crumbIssuer}"
+	                                 descriptors="${h.crumbIssuerDescriptors}"/>
+	        </table>
+	      </f:entry>
+	    </f:optionalBlock>
+      </j:if>
+      
       <f:optionalBlock name="usageStatisticsCollected" checked="${it.usageStatisticsCollected}"
                        title="${%statsBlurb}"
                        help="/help/system-config/usage-statistics.html" />
diff --git a/core/src/main/resources/hudson/model/Hudson/newView.jelly b/core/src/main/resources/hudson/model/Hudson/newView.jelly
index 9cdfe548f9..28b47dc6dc 100644
--- a/core/src/main/resources/hudson/model/Hudson/newView.jelly
+++ b/core/src/main/resources/hudson/model/Hudson/newView.jelly
@@ -1,7 +1,7 @@
 <!--
 The MIT License
 
-Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, id:cactusman
+Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, id:cactusman, Yahoo! Inc.
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -55,6 +55,7 @@ THE SOFTWARE.
         </j:forEach>
 
         <f:block>
+          <f:crumb />
           <input type="submit" name="Submit" value="OK" id="ok" style="margin-left:5em" />
         </f:block>
       </f:form>
diff --git a/core/src/main/resources/hudson/model/UpdateCenter/PageDecoratorImpl/footer.jelly b/core/src/main/resources/hudson/model/UpdateCenter/PageDecoratorImpl/footer.jelly
index 3b4a4633a8..e30118fe9d 100644
--- a/core/src/main/resources/hudson/model/UpdateCenter/PageDecoratorImpl/footer.jelly
+++ b/core/src/main/resources/hudson/model/UpdateCenter/PageDecoratorImpl/footer.jelly
@@ -35,6 +35,8 @@ THE SOFTWARE.
       updateCenter.postBackURL = "${rootURL}/updateCenter/postBack";
       updateCenter.info = { version:"${h.version}" }; 
       updateCenter.url = "${h.updateCenterUrl}";
+      updateCenter.crumbName = "${h.getCrumbRequestField()}";
+      updateCenter.crumb = "${h.getCrumb(request)}";
       Behaviour.addLoadEvent(updateCenter.checkUpdates);
     </script>
   </j:if>
diff --git a/core/src/main/resources/hudson/model/UpdateCenter/index.jelly b/core/src/main/resources/hudson/model/UpdateCenter/index.jelly
index c8abb63918..886559bdca 100644
--- a/core/src/main/resources/hudson/model/UpdateCenter/index.jelly
+++ b/core/src/main/resources/hudson/model/UpdateCenter/index.jelly
@@ -1,7 +1,7 @@
 <!--
 The MIT License
 
-Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Seiji Sogabe
+Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Seiji Sogabe, Yahoo! Inc.
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -47,6 +47,7 @@ THE SOFTWARE.
           window.setTimeout(function() {
               new Ajax.Request("./body", {
                   method: "post",
+                  ${h.getCrumbAsJSONParameterBlock(request)},
                   onSuccess: function(rsp) {
                       var div = document.createElement('div');
                       div.innerHTML = rsp.responseText;
diff --git a/core/src/main/resources/hudson/security/csrf/CrumbIssuer/config.jelly b/core/src/main/resources/hudson/security/csrf/CrumbIssuer/config.jelly
new file mode 100644
index 0000000000..c1329f7366
--- /dev/null
+++ b/core/src/main/resources/hudson/security/csrf/CrumbIssuer/config.jelly
@@ -0,0 +1,36 @@
+<!--
+The MIT License
+
+Copyright (c) 2008-2009, Yahoo! Inc.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+-->
+
+<j:jelly xmlns:j="jelly:core" xmlns:st="jelly:stapler" xmlns:d="jelly:define" xmlns:l="/lib/layout" xmlns:t="/lib/hudson" xmlns:f="/lib/form">
+    <f:entry title="${%Salt}" help="/help/security/csrf/salt.html">
+        <f:textbox name="csrf_crumbSalt" value="${descriptor.crumbSalt}" />
+    </f:entry>
+    <f:entry title="${%Request Field}" help="/help/security/csrf/field.html">
+        <f:textbox name="csrf_crumbField" value="${descriptor.crumbRequestField}" />
+    </f:entry>
+    
+    <j:if test="${!empty(descriptor.subConfigPage)}">
+        <st:include from="${descriptor}" page="${descriptor.subConfigPage}" optional="true" />
+    </j:if>
+</j:jelly>
\ No newline at end of file
diff --git a/core/src/main/resources/hudson/widgets/HistoryWidget/index.jelly b/core/src/main/resources/hudson/widgets/HistoryWidget/index.jelly
index 2673fcd83a..12aaa5c616 100644
--- a/core/src/main/resources/hudson/widgets/HistoryWidget/index.jelly
+++ b/core/src/main/resources/hudson/widgets/HistoryWidget/index.jelly
@@ -1,7 +1,7 @@
 <!--
 The MIT License
 
-Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Seiji Sogabe, id:cactusman
+Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Seiji Sogabe, id:cactusman, Yahoo! Inc.
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -83,6 +83,6 @@ THE SOFTWARE.
     </tr>
   </l:pane>
   <script defer="true">
-    updateBuildHistory("${it.baseUrl}/buildHistory/ajax",${it.nextBuildNumberToFetch});
+    updateBuildHistory("${it.baseUrl}/buildHistory/ajax",${it.nextBuildNumberToFetch},"${h.getCrumbRequestField()}","${h.getCrumb(request)}");
   </script>
 </j:jelly>
\ No newline at end of file
diff --git a/core/src/main/resources/lib/form/crumb.jelly b/core/src/main/resources/lib/form/crumb.jelly
new file mode 100644
index 0000000000..31c7e47853
--- /dev/null
+++ b/core/src/main/resources/lib/form/crumb.jelly
@@ -0,0 +1,11 @@
+<!--
+ Copyright (c) 2008-2009 Yahoo! Inc. 
+ All rights reserved. 
+ The copyrights to the contents of this file are licensed under the MIT License (http://www.opensource.org/licenses/mit-license.php)
+-->
+
+<j:jelly xmlns:j="jelly:core" xmlns:s="jelly:stapler" xmlns:d="jelly:define" xmlns:f="/lib/form">
+  <j:if test="${app.useCrumbs}">
+  	<input type="hidden" name="${h.getCrumbRequestField()}" value="${h.getCrumb(request)}" />
+  </j:if>
+</j:jelly>
\ No newline at end of file
diff --git a/core/src/main/resources/lib/form/submit.jelly b/core/src/main/resources/lib/form/submit.jelly
index 87b025115a..14b4369c3c 100644
--- a/core/src/main/resources/lib/form/submit.jelly
+++ b/core/src/main/resources/lib/form/submit.jelly
@@ -1,7 +1,7 @@
 <!--
 The MIT License
 
-Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi
+Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Yahoo! Inc.
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -22,7 +22,7 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
 -->
 
-<j:jelly xmlns:j="jelly:core" xmlns:s="jelly:stapler" xmlns:d="jelly:define">
+<j:jelly xmlns:j="jelly:core" xmlns:s="jelly:stapler" xmlns:d="jelly:define" xmlns:f="/lib/form">
   <s:documentation>
     Submit button themed by YUI. This should be always
     used instead of the plain &lt;input tag.
@@ -36,5 +36,6 @@ THE SOFTWARE.
       The text of the submit button. Something like "submit", "OK", etc.
     </s:attribute>
   </s:documentation>
+  <f:crumb/>
   <input type="submit" name="${attrs.name ?: 'Submit'}" value="${attrs.value}" class="submit-button" />
 </j:jelly>
\ No newline at end of file
diff --git a/core/src/main/resources/lib/hudson/editableDescription.jelly b/core/src/main/resources/lib/hudson/editableDescription.jelly
index 65131513e9..b4e0f44897 100644
--- a/core/src/main/resources/lib/hudson/editableDescription.jelly
+++ b/core/src/main/resources/lib/hudson/editableDescription.jelly
@@ -1,7 +1,7 @@
 <!--
 The MIT License
 
-Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Tom Huybrechts
+Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Tom Huybrechts, Yahoo! Inc.
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -39,7 +39,7 @@ THE SOFTWARE.
     </div>
 
     <l:hasPermission permission="${permission}">
-      <div align="right"><a href="editDescription" onclick="${h.isAutoRefresh(request) ? null : 'return replaceDescription();'}">
+      <div align="right"><a href="editDescription" onclick="${h.getReplaceDescriptionInvoker(request)}">
         <img src="${imagesURL}/16x16/notepad.gif" alt="" />
         <j:choose>
           <j:when test="${empty(it.description)}">
diff --git a/core/src/main/resources/lib/hudson/executors.jelly b/core/src/main/resources/lib/hudson/executors.jelly
index d40166e9a7..aabf83ae25 100644
--- a/core/src/main/resources/lib/hudson/executors.jelly
+++ b/core/src/main/resources/lib/hudson/executors.jelly
@@ -1,7 +1,7 @@
 <!--
 The MIT License
 
-Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Stephen Connolly, id:cactusman
+Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Stephen Connolly, id:cactusman, Yahoo! Inc.
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -120,7 +120,7 @@ THE SOFTWARE.
     <!-- schedule updates only for the full page reload -->
     <j:if test="${ajax==null and !h.isAutoRefresh(request) and h.hasPermission(app.READ)}">
       <script defer="defer">
-        refreshPart('executors',"${h.hasView(it,'ajaxExecutors')?'.':rootURL}/ajaxExecutors");
+        refreshPart('executors',"${h.hasView(it,'ajaxExecutors')?'.':rootURL}/ajaxExecutors", "${h.getCrumbRequestField()}", "${h.getCrumb(request)}");
       </script>
     </j:if>
 	</l:pane>
diff --git a/core/src/main/resources/lib/hudson/newFromList/form.jelly b/core/src/main/resources/lib/hudson/newFromList/form.jelly
index 929f192db8..a8ce7dfc10 100644
--- a/core/src/main/resources/lib/hudson/newFromList/form.jelly
+++ b/core/src/main/resources/lib/hudson/newFromList/form.jelly
@@ -1,7 +1,7 @@
 <!--
 The MIT License
 
-Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi
+Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Yahoo! Inc.
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -69,6 +69,7 @@ THE SOFTWARE.
        -->
       <input type="radio" name="mode" value="dummy1" style="display:none" />
       <input type="radio" name="mode" value="dummy2" style="display:none" />
+      <s:crumb />
       <input type="submit" name="Submit" value="OK" id="ok" style="margin-left:5em" />
     </s:block>
   </s:form>
diff --git a/core/src/main/resources/lib/hudson/progressiveText.jelly b/core/src/main/resources/lib/hudson/progressiveText.jelly
index ea3a5b8293..777c860121 100644
--- a/core/src/main/resources/lib/hudson/progressiveText.jelly
+++ b/core/src/main/resources/lib/hudson/progressiveText.jelly
@@ -1,7 +1,7 @@
 <!--
 The MIT License
 
-Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi
+Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Yahoo! Inc.
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -44,7 +44,7 @@ THE SOFTWARE.
 	    function fetchNext(e,href) {
 	      new Ajax.Request(href,{
 	          method: "post",
-	          parameters: "start="+e.fetchedBytes,
+	          parameters: {"start":e.fetchedBytes,"${h.getCrumbRequestField()}":"${h.getCrumb(request)}"},
 	          onComplete: function(rsp,_) {
               <!-- append text and do autoscroll if applicable-->
               var stickToBottom = scroller.isSticking();
diff --git a/core/src/main/resources/lib/hudson/project/matrix.jelly b/core/src/main/resources/lib/hudson/project/matrix.jelly
index f41ee18570..231383c527 100644
--- a/core/src/main/resources/lib/hudson/project/matrix.jelly
+++ b/core/src/main/resources/lib/hudson/project/matrix.jelly
@@ -1,7 +1,7 @@
 <!--
 The MIT License
 
-Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi
+Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Yahoo! Inc.
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -94,7 +94,7 @@ THE SOFTWARE.
     </j:choose>
     <j:if test="${ajax==null and attrs.autoRefresh and !h.isAutoRefresh(request)}">
       <script defer="defer">
-        refreshPart('matrix',"./ajaxMatrix");
+        refreshPart('matrix',"./ajaxMatrix","${h.getCrumbRequestField()}","${h.getCrumb(request)}");
       </script>
     </j:if>
   </div>
diff --git a/core/src/main/resources/lib/hudson/queue.jelly b/core/src/main/resources/lib/hudson/queue.jelly
index e50114408c..0dde2f8a60 100644
--- a/core/src/main/resources/lib/hudson/queue.jelly
+++ b/core/src/main/resources/lib/hudson/queue.jelly
@@ -1,7 +1,7 @@
 <!--
 The MIT License
 
-Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Tom Huybrechts
+Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Tom Huybrechts, Yahoo! Inc.
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -82,7 +82,7 @@ THE SOFTWARE.
     <!-- schedule updates only for the full page reload -->
     <j:if test="${ajax==null and !h.isAutoRefresh(request) and h.hasPermission(app.READ)}">
       <script defer="defer">
-        refreshPart('buildQueue',"${h.hasView(it,'ajaxBuildQueue')?'.':rootURL}/ajaxBuildQueue");
+        refreshPart('buildQueue',"${h.hasView(it,'ajaxBuildQueue')?'.':rootURL}/ajaxBuildQueue", "${h.getCrumbRequestField()}", "${h.getCrumb(request)}");
       </script>
     </j:if>
   </l:pane>
diff --git a/test/src/main/java/org/jvnet/hudson/test/HudsonTestCase.java b/test/src/main/java/org/jvnet/hudson/test/HudsonTestCase.java
index 95b6181094..0222931633 100644
--- a/test/src/main/java/org/jvnet/hudson/test/HudsonTestCase.java
+++ b/test/src/main/java/org/jvnet/hudson/test/HudsonTestCase.java
@@ -54,6 +54,8 @@ import hudson.model.AbstractProject;
 import hudson.model.UpdateCenter.UpdateCenterConfiguration;
 import hudson.model.Node.Mode;
 import hudson.scm.SubversionSCM;
+import hudson.security.csrf.CrumbIssuer;
+import hudson.security.csrf.CrumbIssuerDescriptor;
 import hudson.slaves.CommandLauncher;
 import hudson.slaves.DumbSlave;
 import hudson.slaves.RetentionStrategy;
@@ -98,6 +100,7 @@ import javax.servlet.ServletContextEvent;
 
 import junit.framework.TestCase;
 
+import org.apache.commons.httpclient.NameValuePair;
 import org.apache.commons.io.FileUtils;
 import org.apache.commons.io.IOUtils;
 import org.apache.commons.beanutils.PropertyUtils;
@@ -128,8 +131,10 @@ import org.xml.sax.SAXException;
 import com.gargoylesoftware.htmlunit.AjaxController;
 import com.gargoylesoftware.htmlunit.BrowserVersion;
 import com.gargoylesoftware.htmlunit.FailingHttpStatusCodeException;
+import com.gargoylesoftware.htmlunit.HttpMethod;
 import com.gargoylesoftware.htmlunit.Page;
 import com.gargoylesoftware.htmlunit.WebRequestSettings;
+import com.gargoylesoftware.htmlunit.html.DomNode;
 import com.gargoylesoftware.htmlunit.html.HtmlButton;
 import com.gargoylesoftware.htmlunit.html.HtmlForm;
 import com.gargoylesoftware.htmlunit.html.HtmlPage;
@@ -199,6 +204,10 @@ public abstract class HudsonTestCase extends TestCase {
 
         hudson = newHudson();
         hudson.setNoUsageStatistics(true); // collecting usage stats from tests are pointless.
+        
+        hudson.setUseCrumbs(true);
+        hudson.setCrumbIssuer(((CrumbIssuerDescriptor<CrumbIssuer>)Hudson.getInstance().getDescriptor(TestCrumbIssuer.class)).newInstance(null,null));
+
         hudson.servletContext.setAttribute("app",hudson);
         hudson.servletContext.setAttribute("version","?");
         WebAppMain.installExpressionFactory(new ServletContextEvent(hudson.servletContext));
@@ -918,6 +927,30 @@ public abstract class HudsonTestCase extends TestCase {
         public String getContextPath() {
             return "http://localhost:"+localPort+contextPath;
         }
+        
+        /**
+         * Adds a security crumb to the quest
+         */
+        public WebRequestSettings addCrumb(WebRequestSettings req) {
+            NameValuePair crumb[] = { new NameValuePair() };
+            
+            crumb[0].setName(hudson.getCrumbIssuer().getDescriptor().getCrumbRequestField());
+            crumb[0].setValue(hudson.getCrumbIssuer().getCrumb( null ));
+            
+            req.setRequestParameters(Arrays.asList( crumb ));
+            return req;
+        }
+        
+        /**
+         * Creates a URL with crumb parameters relative to {{@link #getContextPath()}
+         */
+        public URL createCrumbedUrl(String relativePath) throws MalformedURLException {
+            CrumbIssuer issuer = hudson.getCrumbIssuer();
+            String crumbName = issuer.getDescriptor().getCrumbRequestField();
+            String crumb = issuer.getCrumb(null);
+            
+            return new URL(getContextPath()+relativePath+"?"+crumbName+"="+crumb);
+        }
     }
 
     // needs to keep reference, or it gets GC-ed.
diff --git a/test/src/main/java/org/jvnet/hudson/test/TestCrumbIssuer.java b/test/src/main/java/org/jvnet/hudson/test/TestCrumbIssuer.java
new file mode 100644
index 0000000000..93e081330e
--- /dev/null
+++ b/test/src/main/java/org/jvnet/hudson/test/TestCrumbIssuer.java
@@ -0,0 +1,55 @@
+/**
+ * Copyright (c) 2008-2009 Yahoo! Inc. 
+ * All rights reserved. 
+ * The copyrights to the contents of this file are licensed under the MIT License (http://www.opensource.org/licenses/mit-license.php)
+ */
+package org.jvnet.hudson.test;
+
+import javax.servlet.ServletRequest;
+
+import net.sf.json.JSONObject;
+
+import org.kohsuke.stapler.StaplerRequest;
+
+import hudson.Extension;
+import hudson.model.ModelObject;
+import hudson.security.csrf.CrumbIssuer;
+import hudson.security.csrf.CrumbIssuerDescriptor;
+
+/**
+ * A crumb issuer that issues a constant crumb value. Used for unit testing.
+ * @author dty
+ */
+public class TestCrumbIssuer extends CrumbIssuer
+{
+    @Override
+    protected String issueCrumb( ServletRequest request, String salt )
+    {
+        return "test";
+    }
+
+    @Override
+    public boolean validateCrumb( ServletRequest request, String salt, String crumb )
+    {
+        return "test".equals(crumb);
+    }
+
+    @Extension
+    public static final class DescriptorImpl extends CrumbIssuerDescriptor<TestCrumbIssuer> implements ModelObject {
+        public DescriptorImpl()
+        {
+            super(null, null);
+            load();
+        }
+
+        @Override
+        public String getDisplayName() {
+            return "Test Crumb";
+        }
+        
+        public TestCrumbIssuer newInstance(StaplerRequest req, JSONObject formData) throws FormException {
+            return new TestCrumbIssuer();
+        }
+    }
+
+}
diff --git a/test/src/test/java/hudson/model/HudsonTest.java b/test/src/test/java/hudson/model/HudsonTest.java
index e2ff5c299b..6f18641b6c 100644
--- a/test/src/test/java/hudson/model/HudsonTest.java
+++ b/test/src/test/java/hudson/model/HudsonTest.java
@@ -1,7 +1,7 @@
 /*
  * The MIT License
  * 
- * Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi
+ * Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Yahoo! Inc.
  * 
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -43,7 +43,7 @@ import org.jvnet.hudson.test.Email;
 import org.jvnet.hudson.test.HudsonTestCase;
 import org.jvnet.hudson.test.recipes.LocalData;
 
-import static javax.servlet.http.HttpServletResponse.SC_BAD_REQUEST;
+import static javax.servlet.http.HttpServletResponse.SC_FORBIDDEN;
 import java.net.URL;
 import java.util.List;
 
@@ -140,7 +140,7 @@ public class HudsonTest extends HudsonTestCase {
             wc.getPage(req);
             fail("Error code expected");
         } catch (FailingHttpStatusCodeException e) {
-            assertEquals(SC_BAD_REQUEST,e.getStatusCode());
+            assertEquals(SC_FORBIDDEN,e.getStatusCode());
         }
 
         // the master computer object should be still here
diff --git a/test/src/test/java/lib/form/ExpandableTextboxTest.java b/test/src/test/java/lib/form/ExpandableTextboxTest.java
index fd3590b493..e3acb0b27e 100644
--- a/test/src/test/java/lib/form/ExpandableTextboxTest.java
+++ b/test/src/test/java/lib/form/ExpandableTextboxTest.java
@@ -1,7 +1,7 @@
 /*
  * The MIT License
  * 
- * Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi
+ * Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Yahoo! Inc.
  * 
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -54,8 +54,8 @@ public class ExpandableTextboxTest extends HudsonTestCase {
      */
     protected HtmlPage evaluateAsHtml(String jellyScript) throws Exception {
         HudsonTestCase.WebClient wc = new WebClient();
-
-        WebRequestSettings req = new WebRequestSettings(new URL(wc.getContextPath()+"eval"), POST);
+        
+        WebRequestSettings req = new WebRequestSettings(wc.createCrumbedUrl("eval"), POST);
         req.setRequestBody("<j:jelly xmlns:j='jelly:core' xmlns:st='jelly:stapler' xmlns:l='/lib/layout' xmlns:f='/lib/form'>"+jellyScript+"</j:jelly>");
         Page page = wc.getPage(req);
         return (HtmlPage) page;
diff --git a/war/resources/WEB-INF/web.xml b/war/resources/WEB-INF/web.xml
index e6025709fd..f5cf546aaa 100644
--- a/war/resources/WEB-INF/web.xml
+++ b/war/resources/WEB-INF/web.xml
@@ -2,7 +2,7 @@
 <!--
 The MIT License
 
-Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Tom Huybrechts, id:digerata
+Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Tom Huybrechts, id:digerata, Yahoo! Inc.
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -49,6 +49,11 @@ THE SOFTWARE.
     <filter-class>hudson.security.HudsonFilter</filter-class>
   </filter>
 
+  <filter>
+    <filter-name>csrf-filter</filter-name>
+    <filter-class>hudson.security.csrf.CrumbFilter</filter-class>
+  </filter>
+  
   <!--
 	The Headers filter allows us to to override headers sent by the container
 	that may be in conflict with what we want.  For example, Tomcat will set
@@ -82,7 +87,11 @@ THE SOFTWARE.
     <filter-name>authentication-filter</filter-name>
     <url-pattern>/*</url-pattern>
   </filter-mapping>
-
+  <filter-mapping>
+    <filter-name>csrf-filter</filter-name>
+    <url-pattern>/*</url-pattern>
+  </filter-mapping>
+  
   <filter>
     <filter-name>plugins-filter</filter-name>
     <filter-class>hudson.util.PluginServletFilter</filter-class>
diff --git a/war/resources/help/security/csrf/field.html b/war/resources/help/security/csrf/field.html
new file mode 100644
index 0000000000..cb6dc75fe5
--- /dev/null
+++ b/war/resources/help/security/csrf/field.html
@@ -0,0 +1,4 @@
+<div>
+  This is name of the request parameter Hudson will look in for a crumb
+  value. 
+</div>
\ No newline at end of file
diff --git a/war/resources/help/security/csrf/salt.html b/war/resources/help/security/csrf/salt.html
new file mode 100644
index 0000000000..fb20b96e49
--- /dev/null
+++ b/war/resources/help/security/csrf/salt.html
@@ -0,0 +1,8 @@
+<div>
+  The salt value is taken as an input to the crumb generation algorithm. It acts
+  as further randomization to complicate dictionary style attacks against the
+  algorithm. In the context of CSRF exploits against Hudson servers, each Hudson
+  server should use a different salt value. If multiple Hudson servers all use
+  a crumb generation algorithm that gets broken, the salt prevents an attacker
+  from running CSRF exploits against all these servers.
+</div>
diff --git a/war/resources/help/system-config/csrf.html b/war/resources/help/system-config/csrf.html
new file mode 100644
index 0000000000..3df24acf16
--- /dev/null
+++ b/war/resources/help/system-config/csrf.html
@@ -0,0 +1,11 @@
+<div>
+  A cross site request forgery (or CSRF/XSRF) is an exploit that enables
+  an unauthorized third party to take actions on a web site as you. In Hudson,
+  this could allow someone to delete jobs, builds or change Hudson's configuration.
+  <p>
+  When this option is enabled, Hudson will check for a generated nonce value, or
+  "crumb", on any request that may cause a change on the Hudson server. This
+  includes any form submission and calls to the remote API.
+  <p>
+  More information about CSRF exploits can be found <a href="http://www.owasp.org/index.php/Cross-Site_Request_Forgery">here</a>.
+</div>
diff --git a/war/resources/scripts/hudson-behavior.js b/war/resources/scripts/hudson-behavior.js
index 2b04bab2be..09e63cfc68 100644
--- a/war/resources/scripts/hudson-behavior.js
+++ b/war/resources/scripts/hudson-behavior.js
@@ -623,13 +623,16 @@ function xor(a,b) {
 }
 
 // used by editableDescription.jelly to replace the description field with a form
-function replaceDescription() {
+function replaceDescription(crumbName,crumb) {
     var d = document.getElementById("description");
     d.firstChild.nextSibling.innerHTML = "<div class='spinner-right'>loading...</div>";
+    var params = new Array(1);
+    params[crumbName] = crumb;
     new Ajax.Request(
         "./descriptionForm",
         {
           method : 'post',
+          parameters : params,
           onComplete : function(x) {
             d.innerHTML = x.responseText;
             Behaviour.applySubtree(d);
@@ -803,10 +806,13 @@ function expandTextArea(button,id) {
 
 // refresh a part of the HTML specified by the given ID,
 // by using the contents fetched from the given URL.
-function refreshPart(id,url) {
+function refreshPart(id,url,crumbName,crumb) {
     var f = function() {
+    	var params = new Array(1);
+    	params[crumbName] = crumb;
         new Ajax.Request(url, {
             method: "post",
+            parameters: params,
             onSuccess: function(rsp) {
                 var hist = $(id);
                 var p = hist.parentNode;
@@ -822,7 +828,7 @@ function refreshPart(id,url) {
                 Behaviour.applySubtree(node);
 
                 if(isRunAsTest) return;
-                refreshPart(id,url);
+                refreshPart(id,url,crumbName,crumb);
             }
         });
     };
@@ -1074,14 +1080,18 @@ function addRadioBlock(id) {
 }
 
 
-function updateBuildHistory(ajaxUrl,nBuild) {
+function updateBuildHistory(ajaxUrl,nBuild,crumbName,crumb) {
     if(isRunAsTest) return;
     $('buildHistory').headers = ["n",nBuild];
 
     function updateBuilds() {
         var bh = $('buildHistory');
+    	var params = new Array(1);
+    	params[crumbName] = crumb;
         new Ajax.Request(ajaxUrl, {
             requestHeaders: bh.headers,
+            method: "post",
+            parameters: params,
             onSuccess: function(rsp) {
                 var rows = bh.rows;
 
@@ -1111,9 +1121,12 @@ function updateBuildHistory(ajaxUrl,nBuild) {
 
 // send async request to the given URL (which will send back serialized ListBoxModel object),
 // then use the result to fill the list box.
-function updateListBox(listBox,url) {
+function updateListBox(listBox,url,crumbName,crumb) {
+	var params = new Array(1);
+	params[crumbName] = crumb;
     new Ajax.Request(url, {
         method: "post",
+        parameters: params,
         onSuccess: function(rsp) {
             var l = $(listBox);
             while(l.length>0)   l.options[0] = null;
@@ -1500,6 +1513,8 @@ function loadScript(href) {
 
 var downloadService = {
     continuations: {},
+    crumbName: null,
+    crumb: null,
 
     download : function(id,url,info, postBack,completionHandler) {
         this.continuations[id] = {postBack:postBack,completionHandler:completionHandler};
@@ -1508,9 +1523,12 @@ var downloadService = {
 
     post : function(id,data) {
         var o = this.continuations[id];
+        var params = new Array(2);
+        params["json"] = Object.toJSON(data);
+        params[downloadService.crumbName] = downloadService.crumb;
         new Ajax.Request(o.postBack, {
             method:"post",
-            parameters:{json:Object.toJSON(data)},
+            parameters:params,
             onSuccess: function() {
                 if(o.completionHandler!=null)
                     o.completionHandler();
@@ -1525,6 +1543,8 @@ var updateCenter = {
     postBackURL : null,
     info: {},
     completionHandler: null,
+    crumbName: null,
+    crumb: null,
     url: "https://hudson.dev.java.net/",
 
     checkUpdates : function() {
@@ -1532,9 +1552,12 @@ var updateCenter = {
     },
 
     post : function(data) {
+    	var params = new Array(2);
+    	params["json"] = Object.toJSON(data);
+    	params[updateCenter.crumbName] = updateCenter.crumb;
         new Ajax.Request(updateCenter.postBackURL, {
             method:"post",
-            parameters:{json:Object.toJSON(data)},
+            parameters:params,
             onSuccess: function() {
                 if(updateCenter.completionHandler!=null)
                     updateCenter.completionHandler();