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Fix remember-me cookie forgery via predictable signature bypass #2

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Fix remember-me cookie forgery via predictable signature bypass #2

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Copilot Feb 18, 2026
c5097ab
Fix critical authentication bypass in TokenBasedRememberMeServices2.m…
Copilot Feb 18, 2026
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5 changes: 3 additions & 2 deletions core/src/main/java/hudson/security/TokenBasedRememberMeServices2.java
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Original file line number Diff line number Diff line change
Expand Up @@ -104,9 +104,10 @@ protected String makeTokenSignature(long tokenExpiryTime, String username) {
UserSeedProperty userSeedProperty = user.getProperty(UserSeedProperty.class);
if (userSeedProperty == null) {
// if you want to filter out the user seed property, you should consider using the DISABLE_USER_SEED instead
return "no-prop";
userSeed = "no-prop";
} else {
userSeed = userSeedProperty.getSeed();
}
userSeed = userSeedProperty.getSeed();
}
String token = String.join(":", username, Long.toString(tokenExpiryTime), userSeed, getKey());
return MAC.mac(token);
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23 changes: 23 additions & 0 deletions test/src/test/java/hudson/security/TokenBasedRememberMeServices2Test.java
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Expand Up @@ -328,6 +328,29 @@ synchronized void verifyInvocations(int count) {
}
}

@Test
void rememberMeToken_forgedWithNoProp_shouldNotAuthenticate() throws Exception {
j.jenkins.setDisableRememberMe(false);

HudsonPrivateSecurityRealm realm = new HudsonPrivateSecurityRealm(false, false, null);
TokenBasedRememberMeServices2 tokenService = (TokenBasedRememberMeServices2) realm.getSecurityComponents().rememberMe2;
j.jenkins.setSecurityRealm(realm);

String username = "alice";
realm.createAccount(username, username);

// Craft a forged remember-me cookie with "no-prop" as the signature
JenkinsRule.WebClient wc = j.createWebClient();
long expiryTime = System.currentTimeMillis() + TimeUnit.DAYS.toMillis(1);
String forgedTokenValue = username + ":" + expiryTime + ":" + "no-prop";
String forgedTokenBase64 = Base64.getEncoder().encodeToString(forgedTokenValue.getBytes(StandardCharsets.UTF_8));
Cookie forgedCookie = new Cookie(j.getURL().getHost(), tokenService.getCookieName(), forgedTokenBase64);
wc.getCookieManager().addCookie(forgedCookie);

// The forged cookie should NOT authenticate the user
assertUserNotConnected(wc, username);
}

private Cookie createRememberMeCookie(TokenBasedRememberMeServices2 tokenService, long deltaDuration, hudson.model.User user) throws Exception {
long tokenValiditySeconds = tokenService.getTokenValiditySeconds();
long expiryTime = System.currentTimeMillis() + TimeUnit.SECONDS.toMillis(tokenValiditySeconds);
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