User impersonation via non-unique JWT cache keys
Published Apr 6, 2026 · Updated Apr 6, 2026
Cache confusion in Nearform fast-jwt before 6.2.0 allows remote authenticated users to receive another valid token's claims. With caching and a collision-prone custom cacheKeyBuilder enabled, src/verifier.js looks up the supplied token by a non-unique key and returns the prior cached payload without binding it to that token or re-verifying it. Default caching and disabled caching are not affected; a collision can apply another user's identity, permissions, or tenant context.
Summary
What happened
Cache confusion in Nearform fast-jwt before 6.2.0 allows remote authenticated users to receive another valid token's claims. With caching and a collision-prone custom cacheKeyBuilder enabled, src/verifier.js looks up the supplied token by a non-unique key and returns the prior cached payload without binding it to that token or re-verifying it. Default caching and disabled caching are not affected; a collision can apply another user's identity, permissions, or tenant context.
The record
- CVE
- CVE-2026-35039
- Published
- Apr 6, 2026
- Updated
- Apr 6, 2026
- Vendor
- Nearform
- Product
- fast-jwt
- Classifications
- CWE-706, CWE-345, CWE-1289, T1550.001
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Apr 6, 2026CVE publishedPublication date reported by the CVE source.
- Apr 6, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=>= 0.0.1, < 6.1.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- GHSA cacheKeyBuilder collision proof of conceptproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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