CVE-2025-6069: HTMLParser quadratic complexity when processing malformed inputs

Medium severity · published Jun 17, 2025

CVE-2025-6069

HTMLParser quadratic complexity when processing malformed inputs

4.3

CVSS

0.6%

EPSS

On KEV

Description

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

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

Attack vector

Network

Complexity

Low

Privileges

Low

User interaction

None

Confidentiality

None

Integrity

None

Availability

Low

Scope

Unchanged

Exploitation

Is it being used?

Exploit prediction (EPSS)0.6% · higher than 49% of CVEs

Exploited in the wildNo evidence yet

CISA KEVNot listed

Ransomware campaign useNot known

Affected products

Which versions

CPython · Python Software Foundation

before 3.9.24; 3.10.0 before 3.10.19; 3.11.0 before 3.11.14; 3.12.0 before 3.12.12; 3.13.0 before 3.13.6; 3.14.0a1 before 3.14.0b3 · source: vendor

Affected product

CPython

Python Software Foundation

All CPython CVEs

References

NVD

https://nvd.nist.gov/vuln/detail/CVE-2025-6069

CVE.org

https://www.cve.org/CVERecord?id=CVE-2025-6069

github.com

https://github.com/python/cpython/commit/4455cbabf991e202185a25a631af206f60bbc949

github.com

https://github.com/python/cpython/commit/6eb6c5dbfb528bd07d77b60fd71fd05d81d45c41

github.com

https://github.com/python/cpython/commit/8d1b3dfa09135affbbf27fb8babcf3c11415df49

github.com

https://github.com/python/cpython/commit/ab0893fd5c579d9cea30841680e6d35fc478afb5

github.com

https://github.com/python/cpython/commit/d851f8e258c7328814943e923a7df81bca15df4b

github.com

https://github.com/python/cpython/commit/f3c6f882cddc8dc30320d2e73edf019e201394fc