CVE-2026-35042

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

State: Published
Severity: 7.5 High
Published: Apr 6, 2026
Updated: Apr 7, 2026
Reserved: Mar 31, 2026

Description

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.

Scores

CVSS	Score	Vector	Source
3.1	7.5 High	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N	GitHub_M

Weaknesses

CWE-345 Insufficient Verification of Data Authenticity
CWE-636 Not Failing Securely ('Failing Open')

Affected Products

Product	Versions
fast-jwtnearform	<= 6.1.0Affected

References

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