CVE-2026-107724: high-severity vulnerability in nearform fast-jwt
fast-jwt treats raw public JWK JSON as an HMAC secret, enabling HS256 token forgery
Published · Updated
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21Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 7.4epss 0.3%
fast-jwt provides fast JSON Web Token (JWT) implementation. In 6.2.4, fast-jwt can classify raw serialized public JWK or JWKS JSON as an HMAC secret because src/crypto.js performDetectPublicKeyAlgorithms treats non-PEM strings as symmetric key material. If HS256 is explicitly allowed or inferred, an attacker who knows the exact serialized public-key bytes can use those bytes as an HMAC key and create a token containing arbitrary claims that createVerifier accepts. Serialization ordering or whitespace differences can prevent exploitation, and applications using supported PEM keys with an asymmetric-only algorithm allowlist are not affected. This issue is fixed in version 6.3.0.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
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-2026-107722CRITICALfast-jwt: Incomplete patch of CVE-2026-34950: Non-whitespace key-prefix re-enables RSA→HS256 algorithm confusionEPSS 0.4%CVE-2026-107721MEDIUMfast-jwt clockTolerance: Infinity silently bypasses both exp and nbf validation (and persists in the verifier cache)EPSS 0.3%