---
id: CVE-2025-69534
title: >-
  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
summary: >-
  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,…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-400
  - CWE-617
vendor: python-markdown
product: markdown
affected:
  - markdown = 3.8
published: '2026-03-05'
updated: '2026-09-07'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-69534'
references:
  - url: 'https://github.com/Python-Markdown/markdown'
    label: cve@mitre.org
  - url: 'https://github.com/Python-Markdown/markdown/actions/runs/15736122892'
    label: cve@mitre.org
  - url: 'https://github.com/Python-Markdown/markdown/issues/1534'
    label: cve@mitre.org
  - url: 'http://www.openwall.com/lists/oss-security/2026/03/06/4'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://access.redhat.com/errata/RHSA-2026:10184'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:13508'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:13512'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:13826'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:14835'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:14873'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:14874'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:19155'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:19366'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:20674'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:20676'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:20677'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:9742'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/security/cve/CVE-2025-69534'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2444839'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2025/cve-2025-69534.json
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2025-69534'
  - url: 'https://github.com/Python-Markdown/markdown/pull/1535'
  - url: >-
      https://github.com/pypa/advisory-database/tree/main/vulns/markdown/PYSEC-2026-89.yaml
tags:
  - nvd
  - osv
  - pip
epss: 0.00566
epssPercentile: 0.44663
ingestedAt: '2026-09-07T14:12:11.009Z'
aliases:
  - GHSA-5wmx-573v-2qwq
  - PYSEC-2026-89
ecosystem: pip
patched:
  - markdown 3.8.1
---

## Overview

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.

## Affected

- `markdown = 3.8`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Package advisory (CVE-2025-69534)

Affected packages:

- `markdown < 3.8.1`

Patched in:

- `markdown 3.8.1`

Source: https://osv.dev/vulnerability/GHSA-5wmx-573v-2qwq