CVE-2025-69534: Python-Markdown Denial of Service via malformed HTML sequences

CVE-2025-69534 · Severity: high · CVSS 7.5 · Published 2026-03-05

Python-Markdown is a popular library used to convert Markdown text into HTML for display in web applications, documentation sites, and automated pipelines. A vulnerability in version 3.8 allows an attacker to crash any application that processes untrusted Markdown by providing specifically malformed text. This can lead to service outages (Denial of Service) and potentially expose internal system information through error messages.

Technologies: Markdown (PyPI). Vendors: PyPI.

Quick answers

Is CVE-2025-69534 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2025-69534 being exploited in the wild.
How severe is CVE-2025-69534?
High severity, with a CVSS score of 7.5, published 5 March 2026.
Which products and versions are affected?
Markdown (PyPI) < 3.8.1, ECOSYSTEM:introduced=0,fixed=3.8.1, ECOSYSTEM:introduced=0,last_affected=3.8.
Is there a fix for CVE-2025-69534?
Yes. Markdown (PyPI): upgrade to 3.8.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2025-69534 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2025-69534?
Check whether you run Markdown (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

  • Markdown (PyPI): upgrade to 3.8.1 or later
    pip install "Markdown>=3.8.1"

Technical details

A Reachable Assertion vulnerability (CWE-617) exists in Python-Markdown version 3.8. When the library processes malformed HTML-like sequences (specifically those starting with '<![') while the 'extra' extension is enabled, it triggers an unhandled AssertionError or 'expected name token' exception from the standard library's html.parser.HTMLParser. Because the library does not catch these exceptions, the entire application process may crash. This allows a remote, unauthenticated attacker to cause a Denial of Service by submitting malicious Markdown content. The issue is a result of a bug in the Python standard library (cpython#77057) for which Python-Markdown has implemented a workaround in version 3.8.1.

Affected products

  • Python-Markdown Project Python-Markdown 3.8

Identifiers

  • CVE-2025-69534
  • GHSA-5wmx-573v-2qwq
  • PYSEC-2026-89

Timeline

  • 2025-06-18: disclosed: Issue reported on GitHub and version 3.8.1 released as a fix
  • 2026-03-05: advisory: NVD published CVE-2025-69534

References

This page as Markdown. Free to reuse under CC BY 4.0 with a link back.