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.
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.
https://www.cve.org/CVERecord?id=CVE-2025-69534 reports: CVE-2025-69534 Published: 2026-03-05 Updated: 2026-03-05
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.
References ----------
https://github.com/Python-Markdown/markdown/issues/1534 https://github.com/Python-Markdown/markdown https://github.com/Python-Markdown/markdown/actions/runs/15736122892 The comments in the linked GitHub issue though note that the root cause is "a bug in the standard lib's HTMLParser which was just fixed last month (see cpython#77057)." and that they are just providing a workaround for older Python versions without that fix yet.
https://github.com/python/cpython/issues/77057 appears to be fixed in 3.13.4 & 3.14.0b2, but doesn't have a security advisory that I've found.
-- -Alan Coopersmith- alan.coopersmith () oracle com Oracle Solaris Engineering - https://blogs.oracle.com/solaris