Authentication bypass via malformed JWT claim validation
Published Feb 4, 2026 · Updated Feb 4, 2026
Type confusion in Keats jsonwebtoken before 10.3.0 allows remote attackers to bypass time-based JWT restrictions with malformed claims. In src/validation.rs, Validation::validate treats exp or nbf values that fail numeric parsing as absent, so enabled checks silently skip them. Exploitation requires an application to validate the affected claim without listing it in required_spec_claims, allowing premature access or acceptance of expired tokens.
Summary
What happened
Type confusion in Keats jsonwebtoken before 10.3.0 allows remote attackers to bypass time-based JWT restrictions with malformed claims. In src/validation.rs, Validation::validate treats exp or nbf values that fail numeric parsing as absent, so enabled checks silently skip them. Exploitation requires an application to validate the affected claim without listing it in required_spec_claims, allowing premature access or acceptance of expired tokens.
The record
- CVE
- CVE-2026-25537
- Published
- Feb 4, 2026
- Updated
- Feb 4, 2026
- Vendor
- Keats
- Product
- jsonwebtoken
- Classifications
- CWE-843
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Feb 4, 2026CVE publishedPublication date reported by the CVE source.
- Feb 4, 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=< 10.3.0
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
- Malformed nbf claim proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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