Shell command execution via post-check %action substitution
Published Apr 13, 2026 · Updated Apr 13, 2026
Command injection in CPython before 3.10.21, 3.11.16, 3.12.14, 3.13.14, 3.14.5rc1, or 3.15.0b1 allows local users to execute shell commands. UnixBrowser.open() checked the raw URL for a dash prefix before replacing %action, so substitution could create a dash-prefixed browser argument that reached the underlying shell. Exploitation requires attacker-controlled URL data containing %action, a susceptible Unix browser controller, and active user interaction.
Summary
What happened
Command injection in CPython before 3.10.21, 3.11.16, 3.12.14, 3.13.14, 3.14.5rc1, or 3.15.0b1 allows local users to execute shell commands. UnixBrowser.open() checked the raw URL for a dash prefix before replacing %action, so substitution could create a dash-prefixed browser argument that reached the underlying shell. Exploitation requires attacker-controlled URL data containing %action, a susceptible Unix browser controller, and active user interaction.
The record
- CVE
- CVE-2026-4786
- Published
- Apr 13, 2026
- Updated
- Apr 13, 2026
- Vendor
- Python Software Foundation
- Product
- CPython
- Classifications
- CWE-88, CWE-77, T1059
- Attack vector
- local
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 13, 2026CVE publishedPublication date reported by the CVE source.
- Apr 13, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=0 <3.15.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
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Weakness, pattern, technique
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Technologies
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Your stack
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