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Critical · 9.1 CVE-2026-34950 EUVD-2026-19356GHSA-mvf2-f6gm-w987

fast-jwt has an incomplete fix for CVE-2023-48223: JWT Algorithm Confusion via Whitespace-Prefixed RSA Public Key

Published Apr 6, 2026 · Updated Apr 6, 2026 · Assigned by GitHub_M

Description

fast-jwt provides fast JSON Web Token (JWT) implementation. In 6.1.0 and earlier, the publicKeyPemMatcher regex in fast-jwt/src/crypto.js uses a ^ anchor that is defeated by any leading whitespace in the key string, re-enabling the exact same JWT algorithm confusion attack that CVE-2023-48223 patched.

Affected products

VendorProductAffectedFixed
nearform fast-jwt <= 6.1.0 —

Affected packages

EcosystemPackageAffectedFixedRecord
npm fast-jwt < 6.2.0 6.2.0 GHSA-mvf2-f6gm-w987

References