PYSEC-2026-89

Vulnerability from pysec - Published: 2026-03-05 15:16 - Updated: 2026-05-21 14:54
VLAI
Details

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.

Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Impacted products
Name purl
markdown pkg:pypi/markdown
Aliases
To clipboard 

{
  "affected": [
    {
      "ecosystem_specific": {},
      "package": {
        "ecosystem": "PyPI",
        "name": "markdown",
        "purl": "pkg:pypi/markdown"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "3.8"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "1.7",
        "2.0",
        "2.0.1",
        "2.0.2",
        "2.0.3",
        "2.1.0",
        "2.1.1",
        "2.2.0",
        "2.2.1",
        "2.3",
        "2.3.1",
        "2.4",
        "2.4.1",
        "2.5",
        "2.5.1",
        "2.5.2",
        "2.6",
        "2.6.1",
        "2.6.10",
        "2.6.11",
        "2.6.2",
        "2.6.3",
        "2.6.4",
        "2.6.5",
        "2.6.6",
        "2.6.7",
        "2.6.8",
        "2.6.9",
        "3.0",
        "3.0.1",
        "3.1",
        "3.1.1",
        "3.2",
        "3.2.1",
        "3.2.2",
        "3.3",
        "3.3.1",
        "3.3.2",
        "3.3.3",
        "3.3.4",
        "3.3.5",
        "3.3.6",
        "3.3.7",
        "3.4",
        "3.4.1",
        "3.4.2",
        "3.4.3",
        "3.4.4",
        "3.5",
        "3.5.1",
        "3.5.2",
        "3.6",
        "3.7",
        "3.8"
      ]
    }
  ],
  "aliases": [
    "CVE-2025-69534",
    "GHSA-5wmx-573v-2qwq"
  ],
  "details": "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.",
  "id": "PYSEC-2026-89",
  "modified": "2026-05-21T14:54:33.726347Z",
  "published": "2026-03-05T15:16:11.243Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/Python-Markdown/markdown/actions/runs/15736122892"
    },
    {
      "type": "ADVISORY",
      "url": "http://www.openwall.com/lists/oss-security/2026/03/06/4"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/Python-Markdown/markdown/issues/1534"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/Python-Markdown/markdown"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-5wmx-573v-2qwq"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}


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Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


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