CVE-2024-5585: PHP proc_open() RCE Vulnerability

CVE-2024-5585 Overview

CVE-2024-5585 is a command injection vulnerability affecting PHP versions 8.1.* before 8.1.29, 8.2.* before 8.2.20, and 8.3.* before 8.3.8. This vulnerability represents an incomplete fix for the previously disclosed CVE-2024-1874. When using the proc_open() command with array syntax on Windows systems, insufficient escaping allows attackers to execute arbitrary commands in the Windows shell if they can control the arguments of the executed command. The bypass occurs when the command name includes trailing spaces, rendering the original CVE-2024-1874 fix ineffective.

Critical Impact

Attackers with control over command arguments can achieve arbitrary command execution on Windows-based PHP servers, potentially leading to complete system compromise, data exfiltration, and lateral movement within affected networks.

Affected Products

• PHP versions 8.1.* before 8.1.29
• PHP versions 8.2.* before 8.2.20
• PHP versions 8.3.* before 8.3.8
• Fedora 40 (via packaged PHP)

Discovery Timeline

• 2024-06-09 - CVE-2024-5585 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-5585

Vulnerability Analysis

This vulnerability stems from an incomplete remediation of CVE-2024-1874, which addressed command injection issues in PHP's proc_open() function on Windows platforms. The original fix implemented argument escaping to prevent malicious input from breaking out of the intended command context. However, researchers discovered that including trailing spaces in the command name bypasses these protections entirely.

When proc_open() is called with array syntax, the function constructs a command string that gets passed to the Windows shell for execution. The escaping mechanism fails to account for edge cases where command names contain trailing whitespace characters. This oversight allows attackers who control command arguments to inject shell metacharacters and execute arbitrary commands with the privileges of the PHP process.

The vulnerability is particularly dangerous in web application contexts where user input may influence command execution parameters, such as file processing utilities, image manipulation tools, or system administration interfaces built with PHP.

Root Cause

The root cause lies in insufficient input sanitization within PHP's command execution handling for Windows environments. The escaping routine implemented to fix CVE-2024-1874 does not properly normalize command names before applying security controls. When a command name ends with trailing spaces, the escaping logic fails to properly isolate the command arguments, allowing shell metacharacters to be interpreted by the Windows command processor rather than being treated as literal string content.

Attack Vector

The attack requires network access to a vulnerable PHP application running on Windows where an attacker can influence arguments passed to proc_open() with array syntax. The attacker crafts malicious input containing shell metacharacters that exploit the trailing space bypass. When the PHP application processes this input through proc_open(), the injected commands execute in the Windows shell context.

For exploitation to succeed, the following conditions must be met:

1. The target system runs a vulnerable PHP version on Windows
2. The application uses proc_open() with array syntax
3. User-controlled input influences the command arguments
4. The command name or execution context allows trailing spaces

The attacker does not require authentication beyond what the target application mandates, making this vulnerability exploitable against any exposed PHP application meeting these criteria.

Detection Methods for CVE-2024-5585

Indicators of Compromise

• Unusual proc_open() calls with trailing spaces in command names appearing in PHP error logs or application logs
• Unexpected child processes spawned by PHP worker processes, particularly command shells (cmd.exe, powershell.exe)
• Anomalous outbound network connections originating from PHP processes
• Evidence of command execution artifacts such as new scheduled tasks, user accounts, or persistence mechanisms

Detection Strategies

• Implement application-level logging for all proc_open(), exec(), and related command execution functions to capture argument patterns
• Deploy endpoint detection rules to monitor for PHP processes spawning unusual child processes on Windows systems
• Use web application firewall (WAF) rules to detect and block requests containing shell metacharacters in parameters likely to reach command execution functions
• Conduct code audits to identify all instances of proc_open() usage with array syntax and assess input validation controls

Monitoring Recommendations

• Monitor PHP process behavior for command shell invocations using process creation telemetry
• Enable and review PHP error logs for warnings related to command execution functions
• Implement file integrity monitoring on critical system directories to detect unauthorized modifications
• Track network connections from web server processes to identify potential data exfiltration or command-and-control activity

How to Mitigate CVE-2024-5585

Immediate Actions Required

• Upgrade PHP immediately to version 8.1.29, 8.2.20, or 8.3.8 or later depending on your installed branch
• Audit all PHP applications for usage of proc_open() with array syntax and implement strict input validation
• Apply the principle of least privilege to PHP processes, limiting their ability to execute system commands
• Consider temporary removal or disabling of functionality that relies on proc_open() until patches are applied

Patch Information

PHP has released security updates addressing this vulnerability. Organizations should upgrade to the following patched versions:

• PHP 8.1.29 or later for the 8.1.x branch
• PHP 8.2.20 or later for the 8.2.x branch
• PHP 8.3.8 or later for the 8.3.x branch

Fedora users should apply updates through their package manager. Additional details are available in the GitHub Security Advisory, Fedora Package Announcements, and the NetApp Security Advisory.

Workarounds

• Implement strict allowlisting of permitted command names and arguments rather than relying on blocklisting
• Normalize all command strings by trimming whitespace before execution
• Use parameterized command execution methods that separate command names from arguments at the API level
• Deploy application-layer controls to validate and sanitize all user input before it reaches command execution functions
• Consider using PHP's escapeshellarg() and escapeshellcmd() functions as an additional defense layer, though these should not be the sole protection

# Example: Verify PHP version and check for vulnerability
php -v
# Ensure version is 8.1.29+, 8.2.20+, or 8.3.8+

# Update PHP on Fedora systems
sudo dnf update php

# Verify the update
php -v