Improper Verification of Cryptographic Signature Affecting fast-jwt package, versions >=6.2.0 <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.
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Test your applications- Snyk IDSNYK-JS-FASTJWT-20825047
- published11 Oct 2026
- disclosed8 Oct 2026
- creditDC INFOSEC, SONG JIHOON
Introduced: 8 Oct 2026
NewCVE-2026-107722 (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 the key-type detection logic in src/crypto.js, where a non-whitespace prefix (control characters, zero-width Unicode, comments, HTTP/PGP wrappers, or similar leading bytes) placed before a PEM header causes the ^-anchored PEM matchers to fail, misclassifying an RSA public key as a raw HMAC secret. An attacker can exploit this to forge an HS256 token whose signature is an HMAC computed with the server's RSA public key, bypassing signature verification entirely.