Authorization bypass via ignored critical JWS headers
Published Sep 22, 2025 · Updated Sep 22, 2025
Improper JWS verification in Authlib before 1.6.4 allows remote attackers to bypass token policies via unknown critical headers. JsonWebSignature.deserialize_compact validates the signature but returns the payload without rejecting or enforcing names listed in the protected crit array. Exploitation requires a service to rely on critical header semantics, such as token binding, and can permit replay or unauthorized privileges.
Summary
What happened
Improper JWS verification in Authlib before 1.6.4 allows remote attackers to bypass token policies via unknown critical headers. JsonWebSignature.deserialize_compact validates the signature but returns the payload without rejecting or enforcing names listed in the protected crit array. Exploitation requires a service to rely on critical header semantics, such as token binding, and can permit replay or unauthorized privileges.
The record
- CVE
- CVE-2025-59420
- Published
- Sep 22, 2025
- Updated
- Sep 22, 2025
- Vendor
- Authlib
- Product
- Authlib
- Classifications
- CWE-345, CWE-863, T1550.001
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 22, 2025CVE publishedPublication date reported by the CVE source.
- Sep 22, 2025Record 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=< 1.6.4
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
- Authlib critical-header bypass cross-runtime PoCproof 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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