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Status published
Medium
CVE-2025-6069
HTMLParser quadratic complexity when processing malformed inputs
Vulnerability Description
The html.parser.HTMLParser class had worse-case quadratic complexity when processing certain crafted malformed inputs potentially leading to amplified denial-of-service.
Impact Analysis
Refer to official advisory for detailed impact metrics.
Remediation
Ensure systems are updated to the latest vendor-supplied patch levels.
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Credits & Attribution
The following person or organization is credited with identifying this vulnerability, as recorded in the NVD database:
- Serhiy Storchaka
- Jake Howard
- sw0rd1ight
References
- https://github.com/python/cpython/issues/135462
- https://github.com/python/cpython/pull/135464
- https://github.com/python/cpython/commit/4455cbabf991e202185a25a631af206f60bbc949
- https://github.com/python/cpython/commit/6eb6c5dbfb528bd07d77b60fd71fd05d81d45c41
- https://github.com/python/cpython/commit/d851f8e258c7328814943e923a7df81bca15df4b
- https://mail.python.org/archives/list/security-announce@python.org/thread/K5PIYLR6EP3WR7ZOKKYQUWEDNQVUXOYM/
- https://github.com/python/cpython/commit/8d1b3dfa09135affbbf27fb8babcf3c11415df49
- https://github.com/python/cpython/commit/ab0893fd5c579d9cea30841680e6d35fc478afb5
- https://github.com/python/cpython/commit/f3c6f882cddc8dc30320d2e73edf019e201394fc
- https://github.com/python/cpython/commit/fdc9d214c01cb4588f540cfa03726bbf2a33fc15
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Affected Vendor
Python Software Foundation
View all reports →Affected Software
CPython
Vulnerable Versions:
0, 3.11.0, 3.12.0, 3.13.0, 3.14.0a1
Timeline
Official Publish:
June 17th, 2025
Last Modified:
April 21st, 2026
Added to House:
July 22nd, 2026
CVSS Vectors
V3:
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L