CVE-2026-34950

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

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

nearform · fast-jwt

CVSS v3.1 GITHUB

9.1 CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS

0.27% chance of exploitation in the next 30 days, 19th percentile

Published

2026-04-06

Proof-of-concept exploits (1)

• advisories/GHSA-mvf2-f6gm-w987

Security advisories

• nearform/fast-jwt/security/advisories/GHSA-mvf2-f6gm-w987

References

• CVE Record
• NVD entry