CVE-2026-107722: critical vulnerability in nearform fast-jwt
fast-jwt: Incomplete patch of CVE-2026-34950: Non-whitespace key-prefix re-enables RSA→HS256 algorithm confusion
Published · Updated
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28Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 9.8epss 0.4%
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/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Affected products
nearform · fast-jwtRelated CVEs — nearform fast-jwt
In the same product, most dangerous first.
CVE-2023-48223MEDIUMfast-jwt JWT Algorithm ConfusionEPSS 0.7%CVE-2025-30144MEDIUMFast-JWT Improperly Validates iss ClaimsEPSS 0.6%CVE-2026-107723HIGHfast-jwt : Silent claim-validator bypass when JWT payload is a JSON arrayEPSS 0.5%CVE-2026-35040MEDIUMfast-jwt: Stateful RegExp (/g or /y) causes non-deterministic allowed-claim validation (logical DoS)EPSS 0.4%CVE-2026-107721MEDIUMfast-jwt clockTolerance: Infinity silently bypasses both exp and nbf validation (and persists in the verifier cache)EPSS 0.3%CVE-2026-107720HIGHfast-jwt: createVerifier accepts unsigned JWTs when key is '' or null and algorithms is explicitly setEPSS 0.3%