CVE-2025-69534: Python-Markdown has an Uncaught Exception
(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.
References
- github.com/Python-Markdown/markdown
- github.com/Python-Markdown/markdown/actions/runs/15736122892
- github.com/Python-Markdown/markdown/issues/1534
- github.com/Python-Markdown/markdown/pull/1535
- github.com/advisories/GHSA-5wmx-573v-2qwq
- github.com/pypa/advisory-database/tree/main/vulns/markdown/PYSEC-2026-89.yaml
- nvd.nist.gov/vuln/detail/CVE-2025-69534
Code Behaviors & Features
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