Python-Markdown has an Uncaught Exception
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.
describes (1)
Related CVEs.
| ID | severity | exploitable | ||
|---|---|---|---|---|
| CVE-2025-69534US | high7.5 | — | ||
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 parsin… | ||||
references
External citations — patches, advisories, analysis.
- http://www.openwall.com/lists/oss-security/2026/03/06/4WEB
- https://github.com/Python-Markdown/markdownWEB
- https://github.com/Python-Markdown/markdown/actions/runs/15736122892WEB
- https://github.com/Python-Markdown/markdown/issues/1534WEB
- https://github.com/Python-Markdown/markdown/pull/1535WEB
- https://github.com/pypa/advisory-database/tree/main/vulns/markdown/PYSEC-2026-89.yamlWEB
- https://nvd.nist.gov/vuln/detail/CVE-2025-69534ADVISORY
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