CVE-2026-28802
CriticalCVSS 9.8Exploitation Probability (EPSS)
Low risk36th percentile - higher than 36% of all known CVEs
Summary
Authlib versions 1.6.5 to 1.6.6 incorrectly passed malicious JWT tokens with 'alg: none' and an empty signature, bypassing signature verification. The issue is fixed in version 1.6.7.
Risk Assessment
An attacker can exploit this vulnerability to forge JWT tokens and gain unauthorized access to OAuth/OpenID Connect systems, potentially leading to account takeover or privilege escalation.
Recommendation
Immediately upgrade Authlib to version 1.6.7 or later. After upgrading, test the JWT verification mechanism in a non-production environment.
Other vulnerabilities in Authlib
See all- CVE-2026-104056Critical
Authlib version 1.7.2 and below contains a vulnerability where discovery JSON metadata is cached without validation or issuer-origin binding. This allows a poisoned discovery response to replace all endpoint values with attacker-controlled values rather than endpoint URLs that share the origin of the configured server metadata URL.
- CVE-2026-96760Critical
Authlib (v1.7.2 and below) contains a signature verification bypass vulnerability. The JsonWebSignature.deserialize_json() method accepts a JSON Serialization JWS object and returns the payload as successfully verified without checking for a signature and without requiring a cryptographic key.
- CVE-2026-27962Critical
A vulnerability in the Authlib library (versions prior to 1.6.9) allows an attacker to inject a JWK key into the JWT header. This enables forging arbitrary JWT tokens that pass signature verification, as the library uses the attacker-supplied key instead of a trusted server key.
- CVE-2026-28498High
A vulnerability was found in the Authlib library (versions before 1.6.9) in the validation of OpenID Connect ID Tokens. The _verify_hash function incorrectly accepts unsupported cryptographic algorithms by returning True instead of rejecting the token. This allows an attacker to bypass token integrity by providing a forged token with an unknown algorithm.
Original NVD description (English source)
Authlib is a Python library which builds OAuth and OpenID Connect servers. From version 1.6.5 to before version 1.6.7, previous tests involving passing a malicious JWT containing alg: none and an empty signature was passing the signature verification step without any changes to the application code when a failure was expected.. This issue has been patched in version 1.6.7.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS