CVE-2004-0542 in PHP
Summary
by MITRE
PHP before 4.3.7 on Win32 platforms does not properly filter all shell metacharacters, which allows local or remote attackers to execute arbitrary code, overwrite files, and access internal environment variables via (1) the "%", "|", or ">" characters to the escapeshellcmd function, or (2) the "%" character to the escapeshellarg function.
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Analysis
by VulDB Data Team • 06/07/2017
This vulnerability resides in the PHP scripting language implementation on Windows platforms prior to version 4.3.7, representing a critical security flaw that directly impacts command execution and system integrity. The issue stems from inadequate filtering of shell metacharacters within PHP's core functions, specifically affecting the escapeshellcmd and escapeshellarg functions that are designed to sanitize user input before passing it to system shell commands. The vulnerability exposes systems to arbitrary code execution attacks through the improper handling of special characters that have meaning within shell environments, creating a pathway for attackers to bypass intended security measures and gain unauthorized access to system resources.
The technical flaw manifests when PHP applications on Win32 systems process user-supplied input through these vulnerable functions. The "%", "|", and ">" characters, when passed to escapeshellcmd, and the "%" character when passed to escapeshellarg, are not properly escaped or filtered, allowing attackers to inject malicious shell commands. This occurs because the functions fail to account for all possible shell metacharacters that could be exploited to manipulate command execution flow. The vulnerability is particularly dangerous on Windows platforms where the command shell behavior differs from Unix-like systems, creating additional attack vectors that are not present in the Linux or Unix implementations of PHP. This flaw falls under the CWE-78 category of "Improper Neutralization of Special Elements used in an OS Command" and aligns with ATT&CK technique T1059.001 for Command and Scripting Interpreter.
The operational impact of this vulnerability extends far beyond simple code execution, as it enables attackers to perform multiple malicious activities including arbitrary code execution, file overwrites, and unauthorized access to system environment variables. Attackers can leverage this vulnerability to execute system commands with the privileges of the web server process, potentially leading to complete system compromise. The ability to overwrite files allows for persistent backdoor installation or data destruction, while access to internal environment variables can reveal sensitive information such as database credentials or system configuration details. This vulnerability affects web applications that rely on user input to construct system commands, making it particularly dangerous in environments where PHP applications handle untrusted input from web users. The attack surface is broad since many web applications use shell command execution for various operations including file management, system monitoring, and external service integration.
Mitigation strategies for this vulnerability require immediate action including upgrading to PHP version 4.3.7 or later where these issues have been resolved through proper shell metacharacter filtering. Organizations should implement input validation and sanitization at multiple layers, ensuring that all user-supplied data passed to shell functions undergoes rigorous filtering before processing. The use of alternative approaches such as PHP's proc_open function with explicit argument arrays instead of shell command construction should be considered to eliminate shell injection risks. Additionally, system administrators should implement proper access controls and privilege separation to limit the impact of successful exploitation attempts. Security monitoring should include detection of suspicious command execution patterns and unusual file access activities. The vulnerability demonstrates the importance of proper input sanitization and the critical need for security updates, as this flaw existed for several years before being properly addressed in the PHP codebase. Organizations should also consider implementing web application firewalls and runtime application self-protection mechanisms to detect and prevent exploitation attempts targeting this and similar vulnerabilities.