diff --git a/changelog.html b/changelog.html
index d7728349ea..0bce7d179b 100644
--- a/changelog.html
+++ b/changelog.html
@@ -67,6 +67,9 @@ Upcoming changes</a>
   <li class='major bug'>
     Since 1.520, Jenkins requires Java 6 or later, breaking Maven builds set to use JDK 5. Now falls back to JVM of slave agent but sets compile/test flags to use defined JDK.
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-18403">issue 18403</a>)
+  <li class='major bug'>
+    Since 1.517, Maven projects using Maven 2 could not build projects using extensions depending on Apache Commons Codec.
+    (<a href="https://issues.jenkins-ci.org/browse/JENKINS-18178">issue 18178</a>)
   <li class=bug>
     Provided maven settings.xml in maven builder is lost.
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-15976">issue 15976</a>)
diff --git a/core/src/main/java/hudson/Util.java b/core/src/main/java/hudson/Util.java
index 31983d5ac1..2e21f8f8ea 100644
--- a/core/src/main/java/hudson/Util.java
+++ b/core/src/main/java/hudson/Util.java
@@ -30,6 +30,7 @@ import edu.umd.cs.findbugs.annotations.SuppressWarnings;
 import hudson.Proc.LocalProc;
 import hudson.model.TaskListener;
 import hudson.os.PosixAPI;
+import hudson.util.IOException2;
 import hudson.util.QuotedStringTokenizer;
 import hudson.util.VariableResolver;
 import hudson.util.jna.WinIOException;
@@ -72,6 +73,7 @@ import java.util.regex.Pattern;
 import hudson.util.jna.Kernel32Utils;
 
 import static hudson.util.jna.GNUCLibrary.LIBC;
+import java.security.DigestInputStream;
 import org.apache.commons.codec.digest.DigestUtils;
 
 /**
@@ -554,11 +556,28 @@ public class Util {
      * @see DigestUtils#md5Hex(InputStream)
      */
     public static String getDigestOf(InputStream source) throws IOException {
+        try {
+            MessageDigest md5 = MessageDigest.getInstance("MD5");
+
+            byte[] buffer = new byte[1024];
+            DigestInputStream in =new DigestInputStream(source,md5);
+            try {
+                while(in.read(buffer)>=0)
+                    ; // simply discard the input
+            } finally {
+                in.close();
+            }
+            return toHexString(md5.digest());
+        } catch (NoSuchAlgorithmException e) {
+            throw new IOException2("MD5 not installed",e);    // impossible
+        }
+        /* JENKINS-18178: confuses Maven 2 runner
         try {
             return DigestUtils.md5Hex(source);
         } finally {
             source.close();
         }
+        */
     }
 
     public static String getDigestOf(String text) {
diff --git a/test/src/test/java/hudson/maven/MavenBuildTest.java b/test/src/test/java/hudson/maven/MavenBuildTest.java
index 11af78c4ec..9dd02c337e 100755
--- a/test/src/test/java/hudson/maven/MavenBuildTest.java
+++ b/test/src/test/java/hudson/maven/MavenBuildTest.java
@@ -8,17 +8,16 @@ import hudson.model.StringParameterDefinition;
 import hudson.tasks.Maven.MavenInstallation;
 import hudson.tasks.test.AbstractTestResultAction;
 import hudson.tasks.test.AggregatedTestResultAction;
-import hudson.tasks.test.TestResultProjectAction;
 
 import java.io.File;
 import java.io.IOException;
-import java.util.List;
 import java.util.Map;
 
 import org.jvnet.hudson.test.Bug;
 import org.jvnet.hudson.test.Email;
 import org.jvnet.hudson.test.ExtractResourceSCM;
 import org.jvnet.hudson.test.HudsonTestCase;
+import org.jvnet.hudson.test.SingleFileSCM;
 
 /**
  * @author Kohsuke Kawaguchi
@@ -177,7 +176,20 @@ public class MavenBuildTest extends HudsonTestCase {
          AbstractTestResultAction<?> testResultAction = moduleBuild.getTestResultAction();
         assertNotNull(testResultAction);
         assertEquals(1, testResultAction.getTotalCount());
-    }    
+    }
+
+    @Bug(18178)
+    public void testExtensionsConflictingWithCore() throws Exception {
+        MavenModuleSet m = createMavenProject();
+        m.setMaven(configureDefaultMaven().getName());
+        m.setScm(new SingleFileSCM("pom.xml",
+                "<project><modelVersion>4.0.0</modelVersion>" +
+                "<groupId>g</groupId><artifactId>a</artifactId><version>0</version>" +
+                "<build><extensions>" +
+                "<extension><groupId>org.springframework.build.aws</groupId><artifactId>org.springframework.build.aws.maven</artifactId><version>3.0.0.RELEASE</version></extension>" +
+                "</extensions></build></project>"));
+        buildAndAssertSuccess(m);
+    }
     
     private static class TestReporter extends MavenReporter {
         private static final long serialVersionUID = 1L;