CVE-2026-35042

Summary

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.

Affected Software

Weaknesses

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

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: poc
  • Automatable: yes
  • Technical Impact: partial

Additional References

• https://github.com/nearform/fast-jwt/security/advisories/GHSA-hm7r-c7qw-ghp6

References

• https://github.com/nearform/fast-jwt/security/advisories/GHSA-hm7r-c7qw-ghp6
• https://www.rfc-editor.org/rfc/rfc7515.html#section-4.1.11

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