CVE-2024-1874: PHP proc_open() RCE Vulnerability

CVE-2024-1874 Overview

CVE-2024-1874 is a critical command injection vulnerability affecting PHP on Windows systems. The vulnerability exists in the proc_open() function when using array syntax for command arguments. Due to insufficient escaping of user-supplied input, attackers who control the arguments passed to an executed command can inject arbitrary commands that will be executed by the Windows shell.

This vulnerability impacts PHP versions 8.1.* before 8.1.28, 8.2.* before 8.2.18, and 8.3.* before 8.3.5, representing a significant attack surface for PHP-based web applications running on Windows servers.

Critical Impact

Attackers can achieve arbitrary command execution on Windows servers running vulnerable PHP versions, potentially leading to complete system compromise, data exfiltration, and lateral movement within affected networks.

Affected Products

• PHP versions 8.1.0 through 8.1.27
• PHP versions 8.2.0 through 8.2.17
• PHP versions 8.3.0 through 8.3.4
• Fedora 39 and Fedora 40 (bundled PHP packages)

Discovery Timeline

• 2024-04-29 - CVE-2024-1874 published to NVD
• 2025-11-04 - Last updated in NVD database

Technical Details for CVE-2024-1874

Vulnerability Analysis

The vulnerability resides in PHP's proc_open() function, which is commonly used to execute external programs and establish communication channels with them. When developers use the array syntax to pass command arguments (a practice recommended for security), PHP is expected to properly escape each argument to prevent shell metacharacter interpretation.

However, the escaping mechanism on Windows platforms contains a critical flaw. The Windows command shell (cmd.exe) interprets certain special characters differently than Unix shells, and PHP's argument escaping logic fails to account for all Windows-specific shell metacharacters and escape sequences.

This allows attackers who can control input that becomes part of command arguments to break out of the intended command context and inject additional commands. The network-accessible nature of most PHP applications combined with the lack of required privileges or user interaction makes this vulnerability particularly dangerous for internet-facing systems.

Root Cause

The root cause of CVE-2024-1874 is improper output encoding (CWE-116) in PHP's process execution layer. When constructing the command line string for Windows process creation, the argument escaping routine does not adequately neutralize shell metacharacters specific to the Windows command interpreter.

Key factors contributing to this vulnerability include:

• Differences between Windows and Unix shell parsing semantics
• Incomplete handling of Windows-specific escape sequences
• Insufficient sanitization of characters that have special meaning in cmd.exe

Attack Vector

The attack vector for CVE-2024-1874 is network-based, requiring no authentication or user interaction. An attacker can exploit this vulnerability by:

1. Identifying a PHP application that uses proc_open() with array syntax where user input influences command arguments
2. Crafting malicious input containing Windows shell metacharacters
3. Submitting this input through the application's normal interface (web forms, API calls, etc.)
4. The malicious payload bypasses PHP's argument escaping and executes in the Windows shell context

The exploitation mechanism involves injecting shell operators and commands that the Windows command interpreter processes after the intended command execution. This can include command chaining operators, output redirection, and arbitrary command execution.

For detailed technical analysis of the exploitation mechanism, refer to the GitHub Security Advisory GHSA-pc52-254m-w9w7 and the CERT Vulnerability ID 123335.

Detection Methods for CVE-2024-1874

Indicators of Compromise

• Unexpected child processes spawned from PHP worker processes (e.g., php-cgi.exe, php.exe)
• Unusual command-line arguments in process execution logs containing shell metacharacters
• Suspicious network connections initiated by PHP processes
• Creation of unexpected files or registry modifications by web server user accounts

Detection Strategies

• Deploy endpoint detection rules to monitor for anomalous process trees originating from PHP executables
• Implement web application firewall (WAF) rules to detect shell metacharacter injection attempts in request parameters
• Enable command-line auditing on Windows servers to capture process creation events with full argument logging
• Review application logs for error messages indicating unexpected shell behavior or command failures

Monitoring Recommendations

• Configure SIEM alerts for process creation events where PHP is the parent and child processes are command interpreters or system utilities
• Monitor for outbound network connections from PHP processes to unexpected destinations
• Track file system changes in web-accessible directories and system locations
• Implement behavioral analysis to detect deviations from normal PHP application execution patterns

How to Mitigate CVE-2024-1874

Immediate Actions Required

• Upgrade PHP to patched versions: 8.1.28+, 8.2.18+, or 8.3.5+
• Audit PHP applications for usage of proc_open(), shell_exec(), exec(), and similar functions
• Implement strict input validation and whitelist-based filtering for any user input used in command execution
• Consider deploying compensating controls such as WAF rules while patching is completed

Patch Information

PHP has released security updates addressing this vulnerability across all affected version branches. Organizations should update to the following minimum versions:

• PHP 8.1.28 or later for the 8.1.x branch
• PHP 8.2.18 or later for the 8.2.x branch
• PHP 8.3.5 or later for the 8.3.x branch

Patch details and source code changes are available in the PHP Security Advisory. Fedora users should apply updates through their package manager as documented in the Fedora Package Announcements.

Workarounds

• Disable or restrict PHP functions that execute system commands using the disable_functions directive in php.ini
• Implement application-level input sanitization that strictly validates and escapes user-controlled data before command execution
• Use alternative approaches to shell command execution where possible, such as native PHP functions or libraries
• Deploy network segmentation to limit the impact of potential compromises on Windows PHP servers

# PHP configuration to disable dangerous functions
# Add to php.ini to restrict command execution capabilities
disable_functions = proc_open,shell_exec,exec,system,passthru,popen,proc_nice,proc_terminate