CVE-2026-4786

Description

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.

References

• https://github.com/python/cpython/commit/c5767a72838a8dda9d6dc5d3558075b055c56bca
• https://github.com/python/cpython/commit/d22922c8a7958353689dc4763dd72da2dea03fff
• https://github.com/python/cpython/commit/f4654824ae0850ac87227fb270f9057477946769
• https://github.com/python/cpython/issues/148169
• https://github.com/python/cpython/pull/148170
• https://mail.python.org/archives/list/security-announce@python.org/thread/JQDUNJVB4AQNTJECSUKOBDU3XCJIPSE5/