Platform
php
Component
composer/composer
Fixed in
2.3.1
1.0.1
2.9.6
CVE-2026-40261 is a Command Injection vulnerability affecting Composer versions between 1.0.0 and 2.9.6. The vulnerability arises from insufficient input validation within the Perforce::syncCodeBase() method, allowing attackers to inject arbitrary commands through a crafted source reference. Successful exploitation could lead to unauthorized code execution and potential system compromise. The vulnerability is fixed in version 2.9.6.
An attacker can exploit CVE-2026-40261 by crafting a malicious source reference containing shell metacharacters. When Composer processes this reference, the Perforce::syncCodeBase() method will append it to a shell command without proper escaping, leading to command execution. Even if Perforce is not installed, Composer will attempt to execute the injected commands. This could allow an attacker to gain control of the system running Composer, potentially exfiltrating sensitive data, installing malware, or disrupting services. The vulnerability shares similarities with CVE-2026-40176, highlighting a broader issue with improper escaping of user-supplied input in Composer's Perforce integration. The blast radius extends to any system utilizing vulnerable Composer versions, particularly in automated build and deployment pipelines.
CVE-2026-40261 was published on 2026-04-15. Its severity is rated as HIGH with a CVSS score of 8.8. The vulnerability is linked to GHSA-wg36-wvj6-r67p and CVE-2026-40176, indicating a related pattern of insecure input handling. Public proof-of-concept (POC) code is likely to emerge given the ease of exploitation and the severity of the vulnerability. The EPSS score is likely to be medium to high, reflecting the potential for widespread exploitation and impact.
Exploit Status
EPSS
0.04% (12% percentile)
CISA SSVC
CVSS Vector
The primary mitigation for CVE-2026-40261 is to upgrade Composer to version 2.9.6 or later. If upgrading is not immediately feasible, consider implementing temporary workarounds. Restrict access to Composer's configuration files and directories to prevent unauthorized modification of source references. Implement strict input validation on any user-supplied data used in Composer commands. While a WAF or proxy cannot directly prevent this vulnerability, they can be configured to detect and block suspicious command patterns. Sigma/YARA rules can be developed to identify potentially malicious Composer configurations or source references. After upgrading, verify the fix by attempting to trigger the vulnerable code path with a crafted source reference; the command should not execute.
Actualice Composer a la versión 2.2.27 o superior (2.2 LTS) o a la versión 2.9.6 (mainline). Como alternativa, evite instalar dependencias desde el código fuente utilizando la opción --prefer-dist o la configuración preferred-install: dist, y solo utilice repositorios de Composer de confianza.
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CVE-2026-40261 is a Command Injection vulnerability in Composer allowing attackers to execute arbitrary commands due to improper escaping of user input.
You are affected if you are using Composer versions between 1.0.0–>= 2.3.0 and < 2.9.6. Check your Composer version and upgrade if necessary.
Upgrade Composer to version 2.9.6 or later to resolve the vulnerability. Implement input validation as a temporary workaround if upgrading is not possible.
While no active campaigns are confirmed, the vulnerability's severity and ease of exploitation suggest it is likely to be targeted. Monitor your systems for suspicious activity.
Refer to the official CVE entry on the NVD website (https://nvd.nist.gov/vuln/detail/CVE-2026-40261) and the Composer security advisory for detailed information.
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