CVE-2026-107722

fast-jwt: Incomplete patch of CVE-2026-34950: Non-whitespace key-prefix re-enables RSA→HS256 algorithm confusion

Published 8 Oct 2026Modified 13 Oct 2026CWE 347

In the Trivy database since at least 24 Oct 2026, 07:11 UTCWhen it arrived before that build is not recorded.

Severity by source

GHSA9.8CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Trivy's own label is CRITICAL. Rated critical by GHSA.

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.

Affected packages and fixed versions

Source	Package	Fixed in
npm::GitHub Security Advisory npm	fast-jwt	6.3.0

References

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