CVE-2026-107723: high-severity vulnerability in nearform fast-jwt
fast-jwt : Silent claim-validator bypass when JWT payload is a JSON array
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21Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 8.1epss 0.5%
fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.3.0, fast-jwt createVerifier accepts a validly signed JWT whose payload is a JSON array because src/decoder.js checks that the payload is an object but does not reject arrays. The claim validator loop then finds no named exp, nbf, iss, aud, sub, jti, or nonce properties and silently skips those configured checks, returning the array as a successfully verified payload. An attacker who can produce or influence a validly signed token may bypass expiry, issuer, audience, subject, revocation, and replay protections. The opt-in requiredClaims option can block missing claims, and signature verification itself is not bypassed. This issue is fixed in version 6.3.0.
CVSS:3.1/AV:N/AC:L/PR:L/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-2026-35040MEDIUMfast-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%CVE-2026-107720HIGHfast-jwt: createVerifier accepts unsigned JWTs when key is '' or null and algorithms is explicitly setEPSS 0.3%