Description
The html.parser.HTMLParser class had worse-case quadratic complexity when processing certain crafted malformed inputs potentially leading to amplified denial-of-service.
References10
- github.com/python/cpython/commit/4455cbabf991e202185a25a631af20…
- github.com/python/cpython/commit/6eb6c5dbfb528bd07d77b60fd71fd0…
- github.com/python/cpython/commit/8d1b3dfa09135affbbf27fb8babcf3…
- github.com/python/cpython/commit/ab0893fd5c579d9cea30841680e6d3…
- github.com/python/cpython/commit/d851f8e258c7328814943e923a7df8…
- github.com/python/cpython/commit/f3c6f882cddc8dc30320d2e73edf01…
- github.com/python/cpython/commit/fdc9d214c01cb4588f540cfa03726b…
- github.com/python/cpython/issues/135462
- github.com/python/cpython/pull/135464
- mail.python.org/archives/list/[email protected]/thre…
Metrics
- CVSS 3.1
-
4.3
MEDIUM
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L - EPSS — exploit probability
- 1% percentile: 49 · as of 7 November 2026
- CWE
- CWE-1333
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.