[SECURITY-4016]

core/src/main/java/hudson/security/SecurityRealm.java

@@ -678,7 +678,9 @@ public abstract class SecurityRealm implements Describable<SecurityRealm>, Exten
             apf.setAuthenticationFailureHandler(new SimpleUrlAuthenticationFailureHandler("/loginError"));
             filters.add(apf);
         }
-        filters.add(new RememberMeAuthenticationFilter(sc.manager2, sc.rememberMe2));
+        final RememberMeAuthenticationFilter rememberMe = new RememberMeAuthenticationFilter(sc.manager2, sc.rememberMe2);
+        rememberMe.setSessionAuthenticationStrategy(new SessionFixationProtectionStrategy());
+        filters.add(rememberMe);
         filters.addAll(commonFilters());
         return new ChainedServletFilter2(filters);
     }

test/src/test/java/hudson/security/SecurityRealmSecurity2371Test.java

@@ -37,9 +37,11 @@ import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
+import org.jvnet.hudson.test.Issue;
 import org.jvnet.hudson.test.JenkinsRule;
 import org.jvnet.hudson.test.MockAuthorizationStrategy;
 import org.jvnet.hudson.test.junit.jupiter.WithJenkins;
+import org.springframework.security.web.authentication.rememberme.AbstractRememberMeServices;
 
 /**
  * Split from {@link SecurityRealmTest} because this is parameterized.
@@ -114,4 +116,51 @@ class SecurityRealmSecurity2371Test {
             System.clearProperty(SecurityRealm.class.getName() + ".sessionFixationProtectionMode");
         }
     }
+
+    @Issue("SECURITY-4016")
+    @ParameterizedTest
+    @MethodSource("modes")
+    void testSessionChangeOnRememberMeAutoLogin(Integer mode) throws Exception {
+        if (mode != null) {
+            System.setProperty(SecurityRealm.class.getName() + ".sessionFixationProtectionMode", String.valueOf(mode));
+        }
+        try {
+            HudsonPrivateSecurityRealm realm = new HudsonPrivateSecurityRealm(false, false, null);
+            j.jenkins.setSecurityRealm(realm);
+            j.jenkins.setDisableRememberMe(false);
+            j.jenkins.setAuthorizationStrategy(new MockAuthorizationStrategy()
+                    .grant(Jenkins.READ).everywhere().toEveryone()
+                    .grant(Jenkins.ADMINISTER).everywhere().to(USERNAME));
+            realm.createAccount(USERNAME, USERNAME);
+
+            // Phase 1: attacker prepares an anonymous session
+            JenkinsRule.WebClient attacker = j.createWebClient();
+            attacker.goTo(""); // establishes anonymous session
+            Cookie attackerSession = attacker.getCookieManager().getCookie(SESSION_COOKIE_NAME);
+
+            // Phase 2: victim logs in with remember-me
+            JenkinsRule.WebClient victim = j.createWebClient();
+            victim.login(USERNAME, USERNAME, true);
+            Cookie rememberMeCookie = victim.getCookieManager()
+                    .getCookie(AbstractRememberMeServices.SPRING_SECURITY_REMEMBER_ME_COOKIE_KEY);
+
+            // Phase 3: victim's session-only cookie disappears (browser restart)
+            // but remember-me persists. Attacker plants their session ID.
+            JenkinsRule.WebClient browser = j.createWebClient();
+            browser.getCookieManager().addCookie(attackerSession);  // planted by sibling page
+            browser.getCookieManager().addCookie(rememberMeCookie); // survives browser restart
+
+            // Phase 4: victim navigates to Jenkins — remember-me auto-login fires
+            browser.goTo("");
+            Cookie postLoginSession = browser.getCookieManager().getCookie(SESSION_COOKIE_NAME);
+
+            // The session must have been rotated
+            assertNotEquals(attackerSession.getValue(), postLoginSession.getValue());
+
+            // Phase 5: replaying the pre-authentication session must not grant access
+            assertThrows(FailingHttpStatusCodeException.class, () -> attacker.goTo("manage"));
+        } finally {
+            System.clearProperty(SecurityRealm.class.getName() + ".sessionFixationProtectionMode");
+        }
+    }
 }