CVE-2026-107720
Prior to 6.3.1, fast-jwt createVerifier accepts an unsigned JWT when key is an empty string or null and algorithms is a non-empty allowlist.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.32%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.3.1, fast-jwt createVerifier accepts an unsigned JWT when key is an empty string or null and algorithms is a non-empty allowlist. Falsy synchronous keys bypass prepareKeyOrSecret, allowedAlgorithms remains active, hasKey is false, and the empty signature avoids the verifySignature gate. An attacker can therefore submit a token containing arbitrary claims without possessing a signing key, resulting in authentication or authorization bypass. Claim validators still run, and non-empty keys, an empty key without algorithms, and the async key resolver path do not have this behavior. This issue is fixed in version 6.3.1.
- CVSS 3.1
- 7.4 HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
- EPSS
- 0.32% probability · 25th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Weakness
- CWE-20, CWE-347
- Source
- security-advisories@github.com
EPSS moved from 0.3% on 9 October 2026 to 0.3% on 26 October 2026.
References
- https://github.com/nearform/fast-jwt/commit/e22a151e83bf6d5e54e281216982d204d5665534
- https://github.com/nearform/fast-jwt/pull/649
- https://github.com/nearform/fast-jwt/releases/tag/v6.3.1
- https://github.com/nearform/fast-jwt/security/advisories/GHSA-8wpc-h4q6-8fxv
- https://github.com/nearform/fast-jwt/security/advisories/GHSA-8wpc-h4q6-8fxv
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.