Improper Verification of Cryptographic Signature Affecting fast-jwt package, versions >=6.2.4 <6.3.0
Threat Intelligence
Snyk has a proof-of-concept or detailed explanation of how to exploit this vulnerability.
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
Do your applications use this vulnerable package?
In a few clicks we can analyze your entire application and see what components are vulnerable in your application, and suggest you quick fixes.
Test your applications- Snyk IDSNYK-JS-FASTJWT-20825049
- published11 Oct 2026
- disclosed8 Oct 2026
- creditCharles Vosburgh
Introduced: 8 Oct 2026
NewCVE-2026-107724 (opens in a new tab)How to fix?
Upgrade fast-jwt to version 6.3.0 or higher.
Overview
fast-jwt is a Fast JSON Web Token implementation
Affected versions of this package are vulnerable to Improper Verification of Cryptographic Signature via performDetectPublicKeyAlgorithms() and performDetectPrivateKeyAlgorithm() in src/crypto.js, when a serialized asymmetric JWK or JWKS is supplied as the verifier's key. Because these functions fall through to a "no PEM header, treat as raw HMAC secret" path, an attacker who knows the public JWK JSON (which is public by design) can compute a valid HS256 signature over arbitrary claims and have it accepted by the verifier, effectively forging tokens with any desired payload.