Improper Verification of Cryptographic Signature Affecting fast-jwt package, versions <6.3.1
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-20825050
- published11 Oct 2026
- disclosed8 Oct 2026
- creditSri Charan
Introduced: 8 Oct 2026
NewCVE-2026-107720 (opens in a new tab)How to fix?
Upgrade fast-jwt to version 6.3.1 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 createVerifier in src/verifier.js, when an empty string or null is passed as the key option. Because the falsy-key branch skipped key preparation, a caller-supplied algorithms allowlist remained active with no key to check against. verifyToken then saw neither a key nor a signature and accepted forged, unsigned tokens as valid, allowing an attacker to bypass signature verification entirely by presenting an unsigned JWT.