Authentication bypass via accepted empty HMAC key
Published Jul 17, 2026 · Updated Jul 17, 2026
Authentication bypass in Authlib joserfc before 1.6.8 allows remote attackers to forge HMAC-signed JWTs when verification uses an empty key. OctKey.import_key accepts zero-length material after only warning, and HMACAlgorithm.verify passes it to hmac.new, making signatures reproducible. The flaw is reachable only when an application supplies an empty or None secret, after which forged identity, role, and scope claims are accepted.
Summary
What happened
Authentication bypass in Authlib joserfc before 1.6.8 allows remote attackers to forge HMAC-signed JWTs when verification uses an empty key. OctKey.import_key accepts zero-length material after only warning, and HMACAlgorithm.verify passes it to hmac.new, making signatures reproducible. The flaw is reachable only when an application supplies an empty or None secret, after which forged identity, role, and scope claims are accepted.
The record
- CVE
- CVE-2026-49852
- Published
- Jul 17, 2026
- Updated
- Jul 17, 2026
- Vendor
- Authlib
- Product
- joserfc
- Classifications
- CWE-287, CWE-1391, CWE-326, T1550.001
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 17, 2026CVE publishedPublication date reported by the CVE source.
- Jul 17, 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=< 1.6.8
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
- Empty-key HMAC JWT forgery procedureproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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