CVE-2026-34950CWE-327

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

Critical · published April 6, 2026

CVSS v3.1
9.1
EPSS
0%
Percentile
18.8
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
9.1 · CRITICAL
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
CVSS v4.0
Not supplied
EPSS
0.00274 · 18.8th percentile
Weakness
CWE-327 · Use of a Broken or Risky Cryptographic Algorithm
Published
2026-04-06T15:54Z
EPSS history
Timeline
  • 06 APR 15:54Z
    fast-jwt has an incomplete fix for CVE-2023-48223: JWT Algorithm Confusion via Whitespace-Prefixed RSA Public Key
    cvelistv5