CVE-2025-69534: in Python-Markdown

Published Mar 5, 2026
·
Updated

Python-Markdown version 3.8 contain a vulnerability where malformed HTML-like sequences can cause html.parser.HTMLParser to raise an unhandled AssertionError during Markdown parsing. Because Python-Markdown does not catch this exception, any application that processes attacker-controlled Markdown may crash. This enables remote, unauthenticated Denial of Service in web applications, documentation systems, CI/CD pipelines, and any service that renders untrusted Markdown. The issue was acknowledged by the vendor and fixed in version 3.8.1. This issue causes a remote Denial of Service in any application parsing untrusted Markdown, and can lead to Information Disclosure through uncaught exceptions.

Affected Software

5 affected componentsFixes available
pypi/markdown=3.8
pip/Markdown<3.8.1
3.8.1
Python-Markdown Markdown Python=3.8
IBM Cognos Analytics<=12.0.4 - 12.0.4 FP2
IBM Cognos Analytics<=12.1.0 - 12.1.3 FP1

Remediation

Recommended actions to resolve this vulnerability, in priority order.

  1. Upgrade

    Upgrade pip/Markdown to a version that resolves this vulnerability.

    Fixed in 3.8.1
  2. Upgrade

    Upgrade Python-Markdown to a version that resolves this vulnerability.

    Fixed in 3.8.1

Event History

Mar 5, 2026
CVE Published
via MITRE·12:00 AM
Data Sourced
via MITRE·12:00 AM
Description
Data Sourced
via NVD·03:16 PM
Description
Data Sourced
via NVD·03:16 PM
SeverityWeaknessAffected Software
Advisory Published
via GitHub·03:30 PM
Data Sourced
via GitHub·03:30 PM
DescriptionWeaknessAffected Software
Data Sourced
via Red Hat·04:01 PM
DescriptionSeverityAffected Software
Sep 11, 2026
Data Sourced
via IBM·12:00 AM
DescriptionAffected Software

Parent advisories

This vulnerability appears in the following advisories.

Frequently Asked Questions

1

What is the severity of CVE-2025-69534?

CVE-2025-69534 has been identified as a critical vulnerability due to the potential for triggering an unhandled AssertionError, which can lead to application crashes.

2

How do I fix CVE-2025-69534?

To mitigate CVE-2025-69534, upgrade Python-Markdown to version 3.8.1 or later.

3

What causes CVE-2025-69534?

CVE-2025-69534 is caused by malformed HTML-like sequences that the html.parser.HTMLParser cannot handle properly.

4

Which versions of Python-Markdown are affected by CVE-2025-69534?

CVE-2025-69534 affects Python-Markdown version 3.8 specifically.

5

What impact does CVE-2025-69534 have on applications?

Applications that utilize Python-Markdown for parsing malformed markdown could experience crashes due to unhandled exceptions.

Contact

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