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Vulnerabilities

Vulnerability · CVE-2026-35042

fast-jwt provides fast JSON Web Token (JWT) implementation.

Published Apr 6, 2026 · catalog updated Jun 17, 2026 · fast-jwt provides fast JSON

Check if you run it

No confirmed exploitation is on record for CVE-2026-35042. EPSS is 0.20%. Act only if a listed version of fast-jwt provides fast JSON is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (fast-jwt provides fast JSON).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
High7.5
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.20%
Remediation
Version ranges on file
Affected products
cpe nearform/fast-jwt · stated fast-jwt

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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe nearform/fast-jwtversion unspecified
  • stated fast-jwt<= 6.1.0

How to fix CVE-2026-35042

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-35042. EPSS is 0.20%. Act only if a listed version of fast-jwt provides fast JSON is installed.

Which versions are affected?

Compare what you have installed with <= 6.1.0. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-345: Insufficient Verification of Data Authenticity; CWE-636. EPSS 0.20%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Apr 6, 2026 · NIST NVD

    Detected

    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.

  2. Jun 17, 2026 · NIST NVD

    Updated

    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.

Sources

  • CVE.orgVulnerability recordCVE-2026-35042

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-35042

    30-day exploitation probability 0.2%

    first.org
  • NIST NVDVulnerability recordCVE-2026-35042

    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

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.