CVE-2025-6069
cpython: Python HTMLParser quadratic complexity
Severity
ModerateRed Hat Product Security
CVSS 3.1
Review impact separately from score.
Published · June 17, 2025
Updated · October 7, 2026
Description
A denial-of-service (DoS) vulnerability has been discovered in Python's html.parser.HTMLParser class. When processing specially malformed HTML input, the parsing runtime can become quadratic with respect to the input size. This significantly increased processing time can lead to excessive resource consumption, ultimately causing a denial-of-service condition in applications that rely on this parser.
CVSS score applicability
The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.
Mitigation
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.
CVSS / CWE
CVSS 3.1 · 4.3CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
CWE-1333 · Inefficient Regular Expression Complexity