Description

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.

Weaknesses 1

Affected Products 1

References 4

• openwall.com http://www.openwall.com/lists/oss-security/2026/03/06/4
  Mailing ListThird Party Advisory
• github.com https://github.com/Python-Markdown/markdown
  Product
• github.com https://github.com/Python-Markdown/markdown/actions/runs/15736122892
  Product
• github.com https://github.com/Python-Markdown/markdown/issues/1534
  ExploitIssue Tracking

Remediation