CVE-2026-4786 PUBLISHED

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

Assigner: PSF
Reserved: 24.03.2026 Published: 13.04.2026 Updated: 14.04.2026

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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CVSS 4.0

CVSS Vector: CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
CVSS Score: 7

Exploitability Metrics		Vulnerable System Impact Metrics		Subsequent System Impact Metrics
Attack Vector	Local	Confidentiality	High	Confidentiality	None
Attack Complexity	Low	Integrity	High	Integrity	None
Attack Requirements	Present	Availability	None	Availability	None
Privileges Required	None
User Interaction	Active

CVSS 4.0

Product Status

Vendor	Python Software Foundation
Product	CPython
Versions	Default: unaffected affected from 0 to 3.15.0 (excl.)

CVE-2026-4786 PUBLISHED

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

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