[oss-security][CVE-2026-4786] CPython: Incomplete mitigation of CVE-2026-4519, %action expansion for command injection to webbrowser.open()

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

-------- Forwarded Message --------
Subject: 	[Security-announce][CVE-2026-4786] Incomplete mitigation of 
CVE-2026-4519, %action expansion for command injection to webbrowser.open()
Date:   Mon, 13 Apr 2026 21:53:53 +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.

Mitgation of CVE-2026-4519 was incomplete. If the URL contained "%action" the
mitigation could be bypassed for certain browser types the "webbrowser.open()"
API could have commands injected into the underlying shell. See CVE-2026-4519
for details.

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

* https://www.cve.org/CVERecord?id=CVE-2026-4786
* https://github.com/python/cpython/pull/148170

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