Vulnerability · Published Apr 6, 2026 · Assigned by GitHub_M

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

Critical 9.1

In plain English

A critical-severity insufficient verification of data authenticity in fast-jwt from nearform. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 12% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)9.1Critical

Exploit odds (30 days)0.2%top 87.9% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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 packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
npm	fast-jwt	6.2.0	GHSA-rp9m-7r4c-75qg

Affected products (as reported)

Vendor	Product	Versions
nearform	fast-jwt	>= 0.0.1, < 6.2.0

Weakness: CWE-345, CWE-706, CWE-1289 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

References

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