CVE-2024-8926: PHP Command Injection RCE Vulnerability

CVE-2024-8926 Overview

CVE-2024-8926 is a command injection vulnerability in PHP that allows attackers to bypass the previous security fixes implemented for CVE-2024-4577. When PHP is deployed on Windows systems with certain non-standard codepage configurations, malicious users can exploit the Windows "Best Fit" codepage behavior to inject arbitrary commands. This vulnerability enables attackers to pass malicious options to the PHP binary, potentially revealing source code of scripts, executing arbitrary PHP code on the server, and compromising the entire web application.

Critical Impact

This vulnerability allows remote attackers with low privileges to achieve full command injection on affected PHP installations running on Windows with non-standard codepage configurations, leading to source code disclosure and arbitrary code execution.

Affected Products

• PHP versions 8.1.* before 8.1.30
• PHP versions 8.2.* before 8.2.24
• PHP versions 8.3.* before 8.3.12

Discovery Timeline

• 2024-10-08 - CVE-2024-8926 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2024-8926

Vulnerability Analysis

This command injection vulnerability (CWE-78) stems from an incomplete fix for the previously disclosed CVE-2024-4577. The original vulnerability addressed Windows "Best Fit" codepage behavior that allowed character substitution to bypass input sanitization. However, under certain non-standard Windows codepage configurations, attackers can still manipulate input to achieve command injection against the PHP binary.

The vulnerability specifically affects PHP-CGI implementations where user-controlled input can be processed through the Windows codepage translation layer before reaching the PHP interpreter. When specific character sequences are submitted, Windows performs character conversion that transforms seemingly benign input into command-line arguments for the PHP binary.

Root Cause

The root cause lies in the Windows operating system's "Best Fit" character conversion behavior combined with incomplete input sanitization in PHP's CGI handling code. When certain codepages are configured on Windows systems, character mappings exist that allow attackers to craft input strings that bypass PHP's argument filtering. After Windows performs its character conversion, these strings become valid command-line switches that PHP interprets as legitimate options, enabling attackers to modify PHP's runtime behavior.

Attack Vector

The attack is network-based and requires only low-privileged access. An attacker can exploit this vulnerability by sending specially crafted HTTP requests to a vulnerable PHP-CGI endpoint. The malicious input leverages Windows codepage conversion to inject arguments like -d (to modify PHP configuration directives) or -s (to display source code). Successful exploitation can lead to:

• Disclosure of PHP source code containing sensitive information
• Execution of arbitrary PHP code with the privileges of the web server
• Complete compromise of the web application and potentially the underlying server

The attack requires no user interaction and can be executed remotely against any exposed PHP-CGI endpoint running on an affected Windows configuration. For detailed technical information about the exploitation mechanism, refer to the GitHub Security Advisory.

Detection Methods for CVE-2024-8926

Indicators of Compromise

• Unusual HTTP requests containing encoded or obfuscated characters targeting PHP-CGI endpoints
• Web server logs showing requests with unexpected query string parameters that could translate to PHP command-line arguments
• Evidence of source code disclosure in response bodies or unexpected PHP configuration changes
• Suspicious process execution patterns showing PHP binary with unexpected command-line arguments

Detection Strategies

• Monitor web application firewall logs for requests containing character sequences commonly used in codepage bypass attacks
• Implement intrusion detection rules to identify requests with unusual Unicode or encoded characters targeting .php endpoints
• Review PHP error logs for unexpected configuration directive changes or source disclosure attempts
• Deploy endpoint detection to monitor PHP process execution for anomalous command-line arguments

Monitoring Recommendations

• Enable detailed logging on web servers to capture full request URLs and query strings for forensic analysis
• Configure SentinelOne Singularity platform to detect and alert on suspicious PHP process behavior and unexpected argument injection
• Implement network traffic analysis to identify patterns consistent with PHP-CGI exploitation attempts
• Establish baseline monitoring for PHP configuration changes and source code access patterns

How to Mitigate CVE-2024-8926

Immediate Actions Required

• Upgrade PHP to patched versions: 8.1.30+, 8.2.24+, or 8.3.12+
• If immediate patching is not possible, consider switching PHP deployment method from CGI to FastCGI or PHP-FPM
• Review Windows codepage configurations on affected servers and consider using standard codepage settings
• Implement web application firewall rules to block suspicious character sequences in requests

Patch Information

PHP has released security updates that address this vulnerability. Organizations should upgrade to the following minimum versions:

• PHP 8.1: Upgrade to version 8.1.30 or later
• PHP 8.2: Upgrade to version 8.2.24 or later
• PHP 8.3: Upgrade to version 8.3.12 or later

Detailed patch information is available in the PHP Security Advisory on GitHub. Additional vendor guidance is available from the NetApp Security Advisory.

Workarounds

• Migrate from PHP-CGI to mod_php, PHP-FPM, or FastCGI configurations which are not affected by this vulnerability
• Configure web server rewrite rules to sanitize or block requests containing potentially dangerous character sequences
• Restrict access to PHP-CGI endpoints using network-level controls or authentication requirements
• Consider implementing a reverse proxy with request filtering capabilities in front of vulnerable PHP installations

# Example: Apache configuration to block potentially malicious requests
# Add to .htaccess or Apache configuration
RewriteEngine On
RewriteCond %{QUERY_STRING} ^[^=]*$ [NC]
RewriteCond %{QUERY_STRING} ^(-|%2D) [NC,OR]
RewriteCond %{QUERY_STRING} ^(-d|%2Dd) [NC]
RewriteRule .* - [F,L]