Vulnerability in Nearform Fast-Jwt
CVE-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 accepts the token instead of rejecting it. This violates the MUST requirement in the RFC.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N.
EPSS exploit prediction
EPSS: 0.002 (9.1th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 9th percentile — 9.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: +0.000
Affected products
- Nearform Fast-Jwt — versions <= 6.1.0
Weakness classification (CWE)
References
- github.com/nearform/fast-jwt/security/advisories/GHSA-hm7r-c7qw-ghp6 (Exploit, Mitigation, Vendor Advisory)
- www.rfc-editor.org/rfc/rfc7515.html (Technical Description)
Frequently asked questions
- What is CVE-2026-35042?
- CVE-2026-35042 is a high-severity vulnerability in Nearform Fast-Jwt, classified under Insufficient Verification of Data Authenticity. CVSS score: 7.5/10. Published 2026-04-06.
- How severe is CVE-2026-35042?
- High severity. CVSS v3 base score is 7.5 out of 10.