CVE-2026-15308

Incremental HTMLParser feed() allows CPU-exhaustion DoS via repeated unterminated markup declarations

Published: 7/9/2026 Last updated: 7/9/2026 Reserved: 7/9/2026

The incremental HTML parser (html.parser.HTMLParser) allows for CPU denial-of-service through repeated unterminated markup declarations when processing uncontrolled data.

CNA assigner: PSF (28c92f92-d60d-412d-b760-e73465c3df22) Requested by: n/a

Metrics

Version	Score	Severity	Vector String
4.0	8.7	High	CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Opam packages affected (7)

conf-python-2-7 conf-python-2-7-dev conf-python-3 conf-python-3-7 conf-python-3-dev py termbox

Products affected (1)

Product	Vendor	Version
CPython	Python Software Foundation	<= 2.0.0

References (8)

https://mail.python.org/archives/list/security-announce@python.org/thread/F6453LWKSHKCTWFLCOURWPLETNUIW2Z5/
https://github.com/python/cpython/pull/153031
https://github.com/python/cpython/issues/153030
https://github.com/python/cpython/commit/07efb08123ba9367a7107325adb9d5626dca1ca9
https://github.com/python/cpython/commit/7933f4bf7131aa4140750f9404f5de0aa2969ced
https://github.com/python/cpython/commit/bcf98ddbc40ec9b3ee87da0124a5660b19b7e606
https://github.com/python/cpython/commit/e9f92ac0b298292e7ff998e52cb8ccacfb27a0bd
http://www.openwall.com/lists/oss-security/2026/07/09/4

Credits (4)

2 Edward-x (https://github.com/YLChen-007)
5 Serhiy Storchaka (https://github.com/serhiy-storchaka)
6 Gregory P. Smith (https://github.com/gpshead)
4 Seth Larson (https://github.com/sethmlarson)