CVE-2026-35042CWE-345CWE-636

fast-jwt accepts unknown `crit` header extensions (RFC 7515 §4.1.11 MUST violation)

High · published April 6, 2026

CVSS v3.1
7.5
EPSS
0%
Percentile
9.2
In the wild
Unconfirmed
What it is

fast-jwt provides fast JSON Web Token (JWT) implementation. In 6.1.0 and earlier, fast-jwt does not validate the crit (Critical) Header Parameter defined in RFC 7515 §4.1.11. When a JWS token contains a crit array listing extensions that fast-jwt does not understand, the library accepts the token instead of rejecting it. This violates the MUST requirement in the RFC.

The record
Technical detail
CVSS v3.1
7.5 · HIGH
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
CVSS v4.0
Not supplied
EPSS
0.00199 · 9.2th percentile
Weaknesses
CWE-345 · Insufficient Verification of Data Authenticity; CWE-636 · Not Failing Securely ('Failing Open')
Published
2026-04-06T17:02Z
EPSS history
Timeline
  • 06 APR 17:02Z
    fast-jwt accepts unknown `crit` header extensions (RFC 7515 §4.1.11 MUST violation)
    cvelistv5