Medium severity · published Apr 9, 2026
CVE-2026-35041
ReDoS in fast-jwt when using RegExp in allowed* leading to CPU exhaustion during token verification
6.5
CVSS
0.3%
EPSS
No
On KEV
Description
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 18% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
FA
fast-jwt · nearform
>= 5.0.0, < 6.2.1 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-35041
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-35041
Patch
https://github.com/nearform/fast-jwt/commit/b0be0ca161593836a153d5180ca5358ad9b5de94
Issue Tracking
https://github.com/nearform/fast-jwt/pull/595
Product
https://github.com/nearform/fast-jwt/releases/tag/v6.2.1
Exploit
https://github.com/nearform/fast-jwt/security/advisories/GHSA-cjw9-ghj4-fwxf
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