[oss-security][CVE-2026-15308] Incremental HTMLParser allows CPU-exhaustion DoS via repeated unterminated markup declarations

[Alan Coopersmith <alan.coopersmith () oracle com>]

https://www.cve.org/CVERecord?id=CVE-2026-15308 currently lists all
versions before Python 3.15.0 as affected.


-------- Forwarded Message --------
Subject:        [Security-announce][CVE-2026-15308] Incremental HTMLParser allows CPU-exhaustion DoS via repeated 
unterminated markup declarations
Date:   Thu, 9 Jul 2026 17:08:21 +0000
From:   Seth Larson <seth () python org>
Reply-To:       security-sig () python org
To:     security-announce () python org



There is a HIGH severity vulnerability affecting CPython.

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

Please see the linked CVE ID for the latest information on affected versions:

* https://www.cve.org/CVERecord?id=CVE-2026-15308
* https://github.com/python/cpython/pull/153031

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