# CVE-2025-61920: PYSEC-2026-1203 - Authlib is vulnerable to Denial of Service via Oversized JOSE Segments

Source: https://junglewise.ai/threats/cve-2025-61920-authlib-is-vulnerable-to-denial-of-service-via-oversized-jose  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-07  
License: CC BY 4.0 with a link back

CVE-2025-61920 · Severity: low · CVSS 3.1 · Published 2026-07-07

Authlib is vulnerable to Denial of Service via Oversized JOSE Segments

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

## Quick answers

**Is CVE-2025-61920 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2025-61920 being exploited in the wild.

**How severe is CVE-2025-61920?** Low severity, with a CVSS score of 3.1, published 7 July 2026.

**Which products and versions are affected?** authlib (PyPI) ECOSYSTEM:introduced=0,fixed=1.6.5.

**Is there a fix for CVE-2025-61920?** Yes. authlib (PyPI): upgrade to 1.6.5 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2025-61920?** 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 1.6.5 or later

  ```sh
  pip install "authlib>=1.6.5"
  ```


## Affected products

- authlib (PyPI) ECOSYSTEM:introduced=0,fixed=1.6.5

## Identifiers

- CVE-2025-61920
- GHSA-pq5p-34cr-23v9
- PYSEC-2026-1203

## 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)