Python CPython "webbrowser.open" "%action" URL injection (CVE-2026-4786)
CVE-2026-4786 Published on April 13, 2026
Incomplete mitigation of CVE-2026-4519, %action expansion for command injection to webbrowser.open()
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.
Weakness Type
What is a Command Injection Vulnerability?
The software constructs all or part of a command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended command when it is sent to a downstream component.
CVE-2026-4786 has been classified to as a Command Injection vulnerability or weakness.
Products Associated with CVE-2026-4786
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Affected Versions
Python Software Foundation CPython:- Before 3.15.0 is affected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.