What’s Vulnerable › Vulnerabilities

CVE-2026-35039: fast-jwt Affected by Cache Confusion via cacheKeyBuilder Collisions Can Return Claims From a Different Token (Identity/Authorization Mixup)

• Severity: critical (CVSS 9.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-04-06 · updated 2026-10-23
• Weakness: CWE-345

Description

fast-jwt provides fast JSON Web Token (JWT) implementation. From 0.0.1 to before 6.2.0, setting up a custom cacheKeyBuilder method which does not properly create unique keys for different tokens can lead to cache collisions. This could cause tokens to be mis-identified during the verification process leading to valid tokens returning claims from different valid tokens and users being mis-identified as other users based on the wrong token. Version 6.2.0 contains a patch.

Affected products

• nearform fast-jwt: from 0.1.0 before 6.1.0 — fixed in 6.1.0

How to fix

Upgrade to a fixed version: nearform fast-jwt 6.1.0. Check the vendor advisory for mitigations.

References

• https://github.com/nearform/fast-jwt/commit/de121056c6415b58770c60640881eaec67ac4ceb
• https://github.com/nearform/fast-jwt/security/advisories/GHSA-rp9m-7r4c-75qg

Get alerted when CVE-2026-35039 or the next vulnerability affects your stack