CVE-2015-4642 in PHP
Summary
by MITRE
The escapeshellarg function in ext/standard/exec.c in PHP before 5.4.42, 5.5.x before 5.5.26, and 5.6.x before 5.6.10 on Windows allows remote attackers to execute arbitrary OS commands via a crafted string to an application that accepts command-line arguments for a call to the PHP system function.
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Analysis
by VulDB Data Team • 05/21/2022
The CVE-2015-4642 vulnerability represents a critical command injection flaw in PHP's Windows implementation that has significant implications for web application security. This vulnerability specifically affects the escapeshellarg function within the ext/standard/exec.c file of PHP, which is designed to escape shell arguments to prevent command injection attacks. The flaw exists in PHP versions prior to 5.4.42, 5.5.26, and 5.6.10, creating a persistent security risk for systems running these outdated versions. The vulnerability is particularly concerning because it allows remote attackers to execute arbitrary operating system commands through crafted input strings that are processed by applications utilizing the PHP system function.
The technical root cause of this vulnerability stems from improper handling of shell argument escaping on Windows platforms. When PHP applications on Windows systems process user input through the escapeshellarg function, the implementation fails to properly sanitize special shell characters that could be used to break out of command contexts. This flaw specifically manifests when applications accept command-line arguments and subsequently call the PHP system function, creating a pathway for attackers to inject malicious commands. The vulnerability is classified under CWE-78 as "Improper Neutralization of Special Elements used in an OS Command," which is a well-documented weakness in command execution contexts.
From an operational perspective, this vulnerability enables attackers to escalate privileges and gain unauthorized access to system resources, potentially leading to complete system compromise. The impact extends beyond simple command execution to include data exfiltration, privilege escalation, and persistent backdoor installation. Attackers can leverage this vulnerability to execute arbitrary code with the privileges of the web server process, which often runs with elevated permissions on the host system. The vulnerability's remote exploitability means that attackers can trigger the malicious code execution without requiring physical access to the system, making it particularly dangerous in web-facing applications.
The attack surface for CVE-2015-4642 includes any PHP application running on Windows platforms that accepts user input and subsequently processes it through system functions. This encompasses content management systems, web applications, and any script that dynamically constructs shell commands based on user-supplied data. The vulnerability aligns with ATT&CK technique T1059.001 for "Command and Scripting Interpreter: PowerShell" and T1059.003 for "Command and Scripting Interpreter: Windows Command Shell," as it enables the execution of arbitrary shell commands through legitimate system interfaces. Organizations should prioritize immediate patching of affected PHP versions and implement additional security controls including input validation, privilege separation, and monitoring for suspicious command execution patterns. The remediation process should also involve comprehensive security audits of all PHP applications to identify and mitigate similar vulnerabilities in the codebase.