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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.

PUBLISHED Reserved 2026-03-31 | Published 2026-04-06 | Updated 2026-04-06 | Assigner GitHub_M




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

Problem types

CWE-327: Use of a Broken or Risky Cryptographic Algorithm

Product status

<= 6.1.0
affected

References

github.com/...st-jwt/security/advisories/GHSA-mvf2-f6gm-w987

cve.org (CVE-2026-34950)

nvd.nist.gov (CVE-2026-34950)

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