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

published 2026-04-03 7 mo ago modified 2026-10-23 16 d ago also EUVD-2026-19380 , GHSA-rp9m-7r4c-75qg

cvss: 9.1; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.2%; EPSS 0.2% chance of exploitation in 30 days, percentile 12%
public exploits: 0; none known

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.

Patch / fix

fixed in 2 links 1

npm fast-jwt 6.2.0
nearform fast-jwt 6.2.0

github.com/nearform/fast-jwt@de12105 commit

CISA SSVC

Exploitation: none
Automatable: yes
Technical impact: total
Assessed: 7 mo ago (2026-04-07)

Exploit prediction

0.22% chance of exploitation in the next 30 days, higher than 12% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	9.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
GitHub	3.1	9.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Affected packages

ecosystem	package	affected	fixed in
npm	fast-jwt	>=0.0.1, <6.2.0	6.2.0

Affected products

nearform fast-jwt

Classification

Weakness

CWE-345 Insufficient Verification of Data Authenticity
CWE-706 Use of Incorrectly-Resolved Name or Reference
CWE-1289 Improper Validation of Unsafe Equivalence in Input

References

github.com /nearform/fast-jwt/commit/de121056c6415b58770c60640881eaec67ac4ceb
web, patch
github.com /nearform/fast-jwt/security/advisories/GHSA-rp9m-7r4c-75qg
web, mitigation, vendor-advisory
nvd.nist.gov /vuln/detail/CVE-2026-35039
advisory
github.com /nearform/fast-jwt
package

Sources

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.

Summary