Improper Verification of Cryptographic Signature Affecting authlib package, versions [,1.6.9)
Threat Intelligence
Snyk has a proof-of-concept or detailed explanation of how to exploit this vulnerability.
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-PYTHON-AUTHLIB-15674452
- published17 Mar 2026
- disclosed16 Mar 2026
- creditPr00fOf3xpl0it, Jay Neiva
Introduced: 16 Mar 2026
CVE-2026-27962 (opens in a new tab)How to fix?
Upgrade authlib to version 1.6.9 or higher.
Overview
authlib is a library in building OAuth and OpenID Connect servers.
Affected versions of this package are vulnerable to Improper Verification of Cryptographic Signature via the JsonWebSignature._prepare_algorithm_key() method in authlib/jose/rfc7515/jws.py. An attacker can bypass authentication and authorization by sending a JWT whose header contains an attacker-controlled jwk while the resolver returns None, causing the library to accept the forged token as valid and expose any embedded claims.