MediumPublic exploit

Signature Verification Bypass in F21 JWT <2.0

IdentifiersCVE-2015-2951CWE-347

A vulnerability in JWT.php in F21 JWT before version 2.0 allows remote attackers to bypass signature verification by submitting specially crafted JWT tokens. The flaw is due to improper validation of the token's signature, enabling attackers to forge tokens that are accepted as valid without possessing the secret key.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Attackers can generate arbitrary JWT tokens that are accepted as valid, potentially leading to authentication bypass, privilege escalation, or unauthorized access to protected resources.

Mitigation

If you can’t patch tonight, do this now.

As an interim measure, restrict acceptance of JWT tokens to those signed with strong algorithms and validate the 'alg' field strictly. Monitor for suspicious authentication attempts and review application logs for signs of token forgery.

Remediation

Patch, then assume compromise.

Upgrade F21 JWT to version 2.0 or later, where proper signature verification is enforced for all JWT tokens.

PUBLIC EXPLOITS

Exploits

1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos.

VALID 1 / 1 TOTALView more in app

ClaimJumperMaturityWeaponizedVerified exploit

Repository is a Python JWT security testing toolkit (“claimjumper”) rather than a single exploit for one product. It provides: (1) JWT decoding and vulnerability analysis with risk scoring (claimjumper/decoder.py, analyzer.py), (2) token forging (alg=none and HS256 with a provided secret) (forger.py), (3) multi-threaded HMAC secret brute forcing for HS256/384/512 using built-in/common secrets and optional wordlists (cracker.py plus wordlists/jwt_secrets.txt; also references a Wallarm wordlist path), (4) an “advanced_attacks” module that generates multiple CVE/pattern-based attack tokens (notably CVE-2022-39227 algorithm confusion, CVE-2018-0114 key injection, CVE-2022-21449 psychic signature, CVE-2020-28042 null signature bypass, plus kid/jku/x5u/jwks spoofing and timestamp tampering), (5) a fuzzing engine with payload libraries for path traversal, SQLi, NoSQLi, command injection, SSRF, etc. (fuzzer.py), and (6) optional live HTTP replay/testing and a playbook-style scanner using `requests` (http_tester.py) that can inject tokens into requests and look for canary/response changes; it logs to jwt_attack.log. The primary entry point is the Click-based CLI (claimjumper/cli.py) exposing commands like analyze, crack, forge/forge-none, advanced-attacks, fuzz, keygen, and full-audit. A standalone local HTML UI (jwt_analyzer.html) provides basic client-side decoding/forging guidance but does not itself perform signing. Overall purpose: generate and test malicious JWT variants against vulnerable JWT verification implementations and assist in auditing JWT configurations.

fevra-devDisclosed Jan 16, 2026pythonhtmllocal (JWT analysis/forgery/cracking) + network (optional live HTTP replay/testing)

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

F21Jwtapplication

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

1 sources tracked across advisories and community write-ups. News coverage will land here when it surfaces.

1 SOURCESView more in app

No news coverage yet. Advisories and community discussion only.

What this page doesn’t show

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Exposure mapping

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Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity1