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OpenAdvisories
High · 8.1 CVE-2026-107723 EUVD-2026-95348GHSA-5hjw-83fp-phq9

fast-jwt : Silent claim-validator bypass when JWT payload is a JSON array

Published Oct 8, 2026 · Updated Oct 14, 2026 · Assigned by GitHub_M

Description

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.

Affected products

VendorProductAffectedFixed
nearform fast-jwt < 6.3.0 —

Affected packages

EcosystemPackageAffectedFixedRecord
npm fast-jwt < 6.3.0 6.3.0 GHSA-5hjw-83fp-phq9

References