CVE-2026-28490

Authlib Vulnerable to JWE RSA1_5 Bleichenbacher Padding Oracle

State: Published
Severity: 8.3 High
Published: Mar 16, 2026
Updated: Mar 16, 2026
Reserved: Feb 27, 2026

Description

Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.9, a cryptographic padding oracle vulnerability was identified in the Authlib Python library concerning the implementation of the JSON Web Encryption (JWE) RSA1_5 key management algorithm. Authlib registers RSA1_5 in its default algorithm registry without requiring explicit opt-in, and actively destroys the constant-time Bleichenbacher mitigation that the underlying cryptography library implements correctly. This issue has been patched in version 1.6.9.

Scores

CVSS	Score	Vector	Source
4.0	8.3 High	CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N	GitHub_M

Weaknesses

CWE-203 Observable Discrepancy
CWE-327 Use of a Broken or Risky Cryptographic Algorithm

Affected Products

Product	Versions
authlibauthlib	< 1.6.9Affected

References

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