CVE-2025-69534
python-markdown: denial of service via malformed HTML-like sequences
Published Mar 5, 2026 · corrected/updated Sep 7, 2026 · Red Hat markdown · evidence confidence high
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.
Grounded briefings
Catalog interpretations for three audiences. Each brief cites ingested metadata and the original advisories below. They are not independent research and they do not invent exploit steps.
Executive
CVE-2025-69534 is a high public vulnerability record for Red Hat markdown. It is not currently listed in the CISA Known Exploited catalog. Check the linked vendor or CERT advisories for patch status. This summary is a catalog interpretation of the ingested metadata and cites the original advisories below.
System administrator
Identify whether Red Hat markdown is in your estate, then compare installed versions with the affected ranges. Affected packages or ranges on record: python-markdown/markdown (3.8). Check the linked vendor or CERT advisories for patch status. Prefer the vendor or distribution advisory linked in Sources before changing production systems. This is a catalog interpretation, not a runbook.
Security analyst
Signals on file: CVSS 8.2, EPSS 0.6%. It is not currently listed in the CISA Known Exploited catalog. Weakness classes: CWE-400, CWE-617. Sources contributing to this record: csaf, cve_org, epss, nvd. Public exploit references, when present, are outbound links only and are not proof of active exploitation. This is a catalog interpretation of stored metadata.
Exploitation and remediation
Exploitation evidence
Not listed as known exploited in CISA KEV. Not in CISA KEV or VulnCheck KEV.
Patch and remediation
No required-action text is stored yet. Use the vendor or CERT links in Sources for patch availability.
Safe detection guidance
Compare installed versions with the affected ranges below and verify the advisory from the original publisher. This site stores metadata and outbound links only; it does not ship exploit code or proof-of-concept payloads.
Code
The project this record applies to. Exploit listings stay in References.
Timeline
Detection, updates, and resolution for this record.
Mar 5, 2026 · NIST NVD
Detected
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 s
Sep 7, 2026 · NIST NVD
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 s
Affected
- cpe python-markdown/markdown3.8
Sources
- CSAF AdvisoriesVendor advisoryRHSA-2026:9742:CVE-2025-69534
A flaw was found in Python-Markdown. Parsing crafted markdown content containing malformed HTML-like sequences causes html.parser.HTMLParser to raise an unhandled AssertionError. This unhandled exception allows an attacker to cause an application crash and potentially disclose se
security.access.redhat.com - CVE.orgVulnerability recordCVE-2025-69534
Official CVE identifier
cve.org - FIRST EPSSExploitation probabilityCVE-2025-69534
30-day exploitation probability 0.6%
first.org - NIST NVDVulnerability recordCVE-2025-69534
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-co
nvd.nist.gov