CVE-2026-35041 json
ReDoS in fast-jwt when using RegExp in allowed* leading to CPU exhaustion during token verification
published 2026-04-09 7 mo ago modified 2026-10-26 13 d ago also EUVD-2026-20899 , GHSA-cjw9-ghj4-fwxf
- cvss
- 4.2
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.3%
- EPSS 0.3% chance of exploitation in 30 days, percentile 19%
- public exploits
- 0
- none known
Summary
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.
Patch / fix
- npm fast-jwt 6.2.1
- nearform fast-jwt 6.2.1
- github.com/nearform/fast-jwt@b0be0ca commit
- github.com/nearform/fast-jwt#595 pull request
- github.com/nearform/fast-jwt/releases/tag/v6.2.1 release
CISA SSVC
- Exploitation
- Proof of concept is public
- Automatable
- no
- Technical impact
- partial
- Assessed
- 7 mo ago
Exploit prediction
0.27% chance of exploitation in the next 30 days, higher than 19% of all scored CVEs (FIRST EPSS, 2026-11-08).
Exploits and checks
- github.com https://github.com/nearform/fast-jwt/security/advisories/GHSA-cjw9-ghj4-fwxf referenced PoC, tagged "exploit" by a source, unverified
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 4.2 | CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:N/I:N/A:H |
| GitHub | 3.1 | 4.2 | CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:N/I:N/A:H |
| NVD | 3.1 | 6.5 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| npm | fast-jwt | >=5.0.0, <6.2.1 |
6.2.1 |
Affected products
- nearform fast-jwt
Classification
- Weakness
-
- CWE-1333 Inefficient Regular Expression Complexity
References
-
github.com
/nearform/fast-jwt/pull/595
web, issue-tracking, patch
-
github.com
/nearform/fast-jwt/commit/b0be0ca161593836a153d5180ca5358ad9b5de94
web, patch
-
github.com
/nearform/fast-jwt/security/advisories/GHSA-cjw9-ghj4-fwxf
exploit, web, mitigation, vendor-advisory
-
github.com
/nearform/fast-jwt/releases/tag/v6.2.1
web, product, release-notes
-
nvd.nist.gov
/vuln/detail/CVE-2026-35041
advisory
-
github.com
/nearform/fast-jwt
package
Sources
- CVE List CVE-2026-35041
- GitHub Advisory GHSA-cjw9-ghj4-fwxf
- NVD CVE-2026-35041
Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.
CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.