CVE-2025-69534
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.
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
Python-Markdown 3.8 crashes on malformed HTML-like input due to an unhandled AssertionError, enabling remote unauthenticated denial of service.
Vulnerability
Description Python-Markdown version 3.8 contains a vulnerability in its handling of HTML-like sequences during Markdown parsing. When the parser encounters malformed <! sequences, such as <! alone or <!> with garbage, the underlying html.parser.HTMLParser raises an unhandled AssertionError [1][3]. Because Python-Markdown does not catch this exception, the entire application crashes.
Attack
Vector An unauthenticated remote attacker can supply crafted Markdown content to any service that uses Python-Markdown to render untrusted input—such as web applications, documentation generators, or CI/CD pipelines—and trigger the crash [1][2]. No special privileges or complex prerequisites are required [1].
Impact
The primary impact is a remote Denial of Service (DoS) caused by application termination. Additionally, uncaught exceptions may leak sensitive information through stack traces if errors are displayed to users [1][3].
Mitigation
The vendor has acknowledged the issue and released the fix in Python-Markdown version 3.8.1 [1][4]. All users should update to the patched version immediately. There is no known exploited vulnerability (KEV) status is not reported [1].
AI Insight generated on May 18, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.
Affected packages
Versions sourced from the GitHub Security Advisory.
| Package | Affected versions | Patched versions |
|---|---|---|
MarkdownPyPI | < 3.8.1 | 3.8.1 |
Affected products
1- Range: < 3.8.1
Patches
0No patches discovered yet.
Vulnerability mechanics
AI mechanics synthesis has not run for this CVE yet.
References
5News mentions
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