---
id: CVE-2025-6069
title: >-
  The html.parser.HTMLParser class had worse-case quadratic complexity when
  processing certain crafted malformed inputs potentially leading to amplified
  denial-of-service.
summary: >-
  The html.parser.HTMLParser class had worse-case quadratic complexity when
  processing certain crafted malformed inputs potentially leading to amplified
  denial-of-service.
severity: medium
cvss: 4.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L'
cwe:
  - CWE-1333
published: '2025-06-17'
updated: '2026-07-30'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-6069'
references:
  - url: >-
      https://github.com/python/cpython/commit/4455cbabf991e202185a25a631af206f60bbc949
    label: cna@python.org
  - url: >-
      https://github.com/python/cpython/commit/6eb6c5dbfb528bd07d77b60fd71fd05d81d45c41
    label: cna@python.org
  - url: >-
      https://github.com/python/cpython/commit/8d1b3dfa09135affbbf27fb8babcf3c11415df49
    label: cna@python.org
  - url: >-
      https://github.com/python/cpython/commit/ab0893fd5c579d9cea30841680e6d35fc478afb5
    label: cna@python.org
  - url: >-
      https://github.com/python/cpython/commit/d851f8e258c7328814943e923a7df81bca15df4b
    label: cna@python.org
  - url: >-
      https://github.com/python/cpython/commit/f3c6f882cddc8dc30320d2e73edf019e201394fc
    label: cna@python.org
  - url: >-
      https://github.com/python/cpython/commit/fdc9d214c01cb4588f540cfa03726bbf2a33fc15
    label: cna@python.org
  - url: 'https://github.com/python/cpython/issues/135462'
    label: cna@python.org
  - url: 'https://github.com/python/cpython/pull/135464'
    label: cna@python.org
  - url: >-
      https://mail.python.org/archives/list/security-announce@python.org/thread/K5PIYLR6EP3WR7ZOKKYQUWEDNQVUXOYM/
    label: cna@python.org
tags:
  - nvd
epss: 0.00589
epssPercentile: 0.46886
ingestedAt: '2026-07-31T06:58:50.948Z'
---

## Overview

The html.parser.HTMLParser class had worse-case quadratic complexity when processing certain crafted malformed inputs potentially leading to amplified denial-of-service.

## Remediation

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