Vulnerability in Nearform Fast-Jwt
CVE-2026-35041
fast-jwt provides fast JSON Web Token (JWT) implementation. From 5.0.0 to 6.2.0, a denial-of-service condition exists in fast-jwt when the allowedAud verification option is configured using a regular expression. Because the aud claim is attacker-controlled and the library evaluates it against the supplied RegExp, a crafted JWT can trigger catastrophic backtracking in the JavaScript regex engine, resulting in significant CPU consumption during verification. This vulnerability is fixed in 6.2.1.
Vulnerability class: ReDoS (Regular Expression Denial of Service)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 4.2 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:N/I:N/A:H.
EPSS exploit prediction
EPSS: 0.004 (34.6th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 35th percentile — 34.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.004 · change: +0.002
Affected products
- Nearform Fast-Jwt — versions >= 5.0.0, < 6.2.1
Weakness classification (CWE)
References
- github.com/nearform/fast-jwt/security/advisories/GHSA-cjw9-ghj4-fwxf (Exploit, Mitigation, Vendor Advisory)
- github.com/nearform/fast-jwt/pull/595 (Patch, Issue Tracking)
- github.com/nearform/fast-jwt/commit/b0be0ca161593836a153d5180ca5358ad9b5de94 (Patch)
- github.com/nearform/fast-jwt/releases/tag/v6.2.1 (Product, Release Notes)
Frequently asked questions
- What is CVE-2026-35041?
- CVE-2026-35041 is a medium-severity vulnerability in Nearform Fast-Jwt, classified under Inefficient Regular Expression Complexity. CVSS score: 4.2/10. Published 2026-04-09.
- How severe is CVE-2026-35041?
- Medium severity. CVSS v3 base score is 4.2 out of 10.