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The nonce was random.nextInt(3) used as an index into a 3-element array, so only 3 possible values ever existed - an attacker could brute-force a valid nonce in at most 3 tries without ever touching the victim's session. Switched to utils.Hash.randomString(), matching the real-random pattern already used correctly in CsrfChallengeTargetFour/Seven. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
🏆 Security Shepherd — CTF Patch Score0 / 40 challenges patched
Commit: No points yet — this commit didn't solve any challenges, so there's nothing on the leaderboard for it. Patch a vulnerability and push again! 💪 |
The weak-nonce fix in this branch only addressed CsrfChallengeTargetSix's
own token generation (random.nextInt(3) -> Hash.randomString()), but left
CsrfChallengeSixGetToken untouched: it took the userId to look up from a
request parameter instead of the caller's own session, and matched it with
LIKE (wildcard metacharacters unescaped) instead of an exact match - letting
any user fetch any other user's real CSRF token directly, completely
defeating the point of the token being unpredictable. Same bug class,
same fix, as the equivalent endpoint already fixed for CSRF Challenge Seven.
Scoped the lookup to the caller's own session userId
(ses.getAttribute("userStamp")) and switched LIKE to an exact match.
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Summary
The nonce was
random.nextInt(3)used as an index into a 3-element hardcoded array, so only 3 possible values ever existed.Fix
Switched to
utils.Hash.randomString().Test plan
mvn compile,mvn spotless:checkclean, full test suite passes🤖 Generated with Claude Code