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

Source: https://junglewise.ai/threats/cve-2026-28490-authlib-vulnerable-to-jwe-rsa1-5-bleichenbacher-padding-oracle  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-03-16  
License: CC BY 4.0 with a link back

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)](https://junglewise.ai/threats/technologies/authlib). Vendors: [PyPI](https://junglewise.ai/threats/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

  ```sh
  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

## Related threats

- [Authlib client configuration endpoint authorization bypass](https://junglewise.ai/threats/cve-2026-116672-authlib-is-a-python-library-which-builds-oauth-and-openid)
- [Authlib RFC 9101 server-side request forgery in request_uri parameter](https://junglewise.ai/threats/cve-2026-114620-authlib-is-a-python-library-which-builds-oauth-and-openid)
- [Authlib OpenID Connect scope validation bypass](https://junglewise.ai/threats/cve-2026-114619-authlib-is-a-python-library-which-builds-oauth-and-openid)
- [Authlib JWT Bearer Grant audience validation bypass](https://junglewise.ai/threats/cve-2026-114618-authlib-is-a-python-library-which-builds-oauth-and-openid)
- [Authlib nonce validation bypass in OpenID token parsing](https://junglewise.ai/threats/cve-2026-114617-authlib-is-a-python-library-which-builds-oauth-and-openid)