CVE-2026-107722
An attacker who knows the public key bytes can sign arbitrary HS256 claims with that public material when HS256 is inferred or allowed, resulting in authentication or authorization bypass.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.36%). 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. From 6.2.0 until 6.3.0, fast-jwt can misclassify RSA public-key text as an HMAC secret when the key has non-whitespace content before its PEM header. In src/crypto.js, performDetectPublicKeyAlgorithms trims whitespace but publicKeyPemMatcher remains start-anchored, so comments, control characters, zero-width characters, or wrapper text can prevent PEM detection and reach the HMAC fallback. An attacker who knows the public key bytes can sign arbitrary HS256 claims with that public material when HS256 is inferred or allowed, resulting in authentication or authorization bypass. An asymmetric-only algorithm allowlist prevents the attack. This issue is fixed in version 6.3.0.
- CVSS 3.1
- 9.8 CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- EPSS
- 0.36% probability · 29th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Weakness
- CWE-347
- Source
- security-advisories@github.com
EPSS moved from 0.3% on 9 October 2026 to 0.4% on 26 October 2026.
References
- https://github.com/nearform/fast-jwt/commit/d96bbc6c5336055a6dbfa318fdbab01197264cfa
- https://github.com/nearform/fast-jwt/pull/632
- https://github.com/nearform/fast-jwt/releases/tag/v6.3.0
- https://github.com/nearform/fast-jwt/security/advisories/GHSA-ww5h-9m49-7xx4
- https://github.com/nearform/fast-jwt/security/advisories/GHSA-ww5h-9m49-7xx4
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.