Recent updates have been released for PHP Composer to fix two critical vulnerabilities that could allow command execution on systems. As a widely-used tool for dependency management among developers, any such flaws pose significant security risks.
Details of the Vulnerabilities
The vulnerabilities are found in the Perforce Version Control System (VCS) driver, potentially enabling attackers to run arbitrary commands on the affected system. Developers are advised to update to Composer version 2.9.6 or the long-term support version 2.2.27 immediately.
According to Nils Adermann’s security advisory, these issues arise from improper handling of shell commands, leading to potential exploitation.
Fortunately, there have been no reports of these vulnerabilities being exploited in the wild prior to the advisory’s publication.
Exploring the Security Flaws
The flaws present significant risks to developers, especially when dealing with untrusted projects or malicious package metadata.
CVE-2026-40176: Identified by saku0512, this vulnerability affects how Perforce commands are generated, allowing attackers to inject commands by altering connection parameters in a malicious composer.json file. Notably, this requires manual execution of Composer commands in an untrusted directory.
CVE-2026-40261: Discovered by Koda Reef, this flaw involves improper escaping of a system shell command parameter. It can be exploited without needing Perforce installed on the target machine, posing a high risk when malicious dependencies are installed.
Protective Measures and Recommendations
Security teams have proactively scanned major repositories like Packagist.org and Private Packagist, finding no current exploitation of these vulnerabilities. Publication of Perforce source metadata has been disabled on these platforms since April 10, 2026, as a precaution.
The most effective mitigation is to update Composer immediately using the command composer.phar self-update in the terminal. If immediate updates are not possible, consider these temporary measures:
- Use the
--prefer-distflag to avoid installing from source. - Rely solely on trusted Composer package repositories.
- Examine composer.json files of untrusted projects carefully, ensuring all fields related to Perforce are valid.
Developers using self-hosted Private Packagist solutions should expect updates soon, including tools for scanning malicious metadata.
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