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Vulnerabilities

Vulnerability · CVE-2025-69534

python-markdown: denial of service via malformed HTML-like sequences

Published Mar 5, 2026 · catalog updated Sep 7, 2026 · Red Hat

Check if you run it

No confirmed exploitation is on record for CVE-2025-69534. EPSS is 0.59%. Act only if a listed version of Red Hat is installed.

Gaps on this record

  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
High8.2
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.59%
Remediation
Advisory link
Affected products
cpe python-markdown/markdown

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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe python-markdown/markdown3.8

How to fix CVE-2025-69534

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2025-69534. EPSS is 0.59%. Act only if a listed version of Red Hat is installed.

Which versions are affected?

Compare what you have installed with 3.8. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-400: Uncontrolled Resource Consumption; CWE-617. EPSS 0.59%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. 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

  2. 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

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

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.