CVE-2026-28490: Authlib Vulnerable to JWE RSA1_5 Bleichenbacher Padding Oracle

CVE-2026-28490 · Severity: medium · CVSS 4 · Published 2026-03-16

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.

Technologies: authlib (PyPI). Vendors: PyPI.

Quick answers

Is CVE-2026-28490 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-28490 being exploited in the wild.
How severe is CVE-2026-28490?
Medium severity, with a CVSS score of 4, published 16 March 2026.
Which products and versions are affected?
authlib (PyPI) ECOSYSTEM:introduced=0,fixed=1.6.9.
Is there a fix for CVE-2026-28490?
Yes. authlib (PyPI): upgrade to 1.6.9 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
Am I affected by CVE-2026-28490?
Check whether you run authlib (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • authlib (PyPI): upgrade to 1.6.9 or later
    pip install "authlib>=1.6.9"

Affected products

  • authlib (PyPI) ECOSYSTEM:introduced=0,fixed=1.6.9

Identifiers

  • CVE-2026-28490
  • GHSA-7432-952r-cw78
  • PYSEC-2026-2116

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