python -- more webbrowser.open() command injection vulnerabilities

Seth Larson reports:

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

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.

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