CVE-2024-51736: Sensiolabs Symfony RCE Vulnerability

CVE-2024-51736 Overview

CVE-2024-51736 is a command injection vulnerability affecting the Symfony PHP framework's Process component on Windows systems. The vulnerability exists because when an executable file named cmd.exe is located in the current working directory, it will be called by the Process class when preparing command arguments, leading to possible command hijacking. This is a classic example of a DLL hijacking attack pattern applied to executable resolution, exploiting Windows' search order for executables.

Critical Impact

Attackers can achieve arbitrary command execution by placing a malicious cmd.exe in the application's working directory, potentially leading to complete system compromise.

Affected Products

• Sensiolabs Symfony versions prior to 5.4.46
• Sensiolabs Symfony versions 6.x prior to 6.4.14
• Sensiolabs Symfony versions 7.x prior to 7.1.7
• Microsoft Windows (as the vulnerable platform)

Discovery Timeline

• 2024-11-06 - CVE-2024-51736 published to NVD
• 2025-09-04 - Last updated in NVD database

Technical Details for CVE-2024-51736

Vulnerability Analysis

This vulnerability falls under CWE-77 (Improper Neutralization of Special Elements used in a Command), commonly known as Command Injection. The Symfony Process component is designed to execute commands in sub-processes, providing a cross-platform abstraction for process management in PHP applications.

The root issue lies in how Windows resolves executable paths. When the Process class prepares command arguments on Windows, it may invoke cmd.exe without specifying an absolute path. Windows' executable search order prioritizes the current working directory before the system PATH, meaning a malicious cmd.exe placed in the application's working directory would be executed instead of the legitimate system binary.

This vulnerability can be exploited without authentication and requires no user interaction. The attack can be performed over the network if an attacker can influence the contents of the application's working directory—for instance, through file upload functionality or other file-writing vulnerabilities.

Root Cause

The Symfony Process component relies on the Windows shell (cmd.exe) when preparing and executing commands. The vulnerability stems from the component not using an absolute path to the system's cmd.exe binary (typically C:\Windows\System32\cmd.exe). Instead, it relies on Windows' executable resolution mechanism, which follows a predictable search order that includes the current working directory before system directories.

Attack Vector

The attack requires an adversary to place a malicious executable named cmd.exe in the current working directory of the vulnerable Symfony application. This could be accomplished through:

1. Exploiting a file upload vulnerability in the same application
2. Leveraging another vulnerability that allows writing files to the application directory
3. Social engineering an administrator to place the file
4. Compromising a shared hosting environment where multiple applications share directories

Once the malicious cmd.exe is in place, any subsequent use of the Symfony Process component will execute the attacker-controlled binary instead of the legitimate Windows command interpreter, granting arbitrary code execution with the privileges of the PHP process.

The vulnerability mechanism involves the Symfony Process class invoking cmd.exe during command preparation without specifying an absolute path. On Windows, executable resolution checks the current working directory before system paths, allowing a malicious binary to be executed. For detailed technical analysis, refer to the GitHub Security Advisory.

Detection Methods for CVE-2024-51736

Indicators of Compromise

• Presence of unexpected cmd.exe files outside of C:\Windows\System32\ directory
• Unusual process execution chains where PHP spawns a cmd.exe from a non-standard location
• File creation events for executables in web application directories
• Anomalous network connections originating from PHP worker processes

Detection Strategies

• Monitor file system events for creation of executable files (.exe, .bat, .cmd) in web application directories
• Implement application whitelisting to prevent execution of binaries from non-standard locations
• Deploy endpoint detection rules to alert on process execution from web-accessible directories
• Use SentinelOne's behavioral AI to detect anomalous process spawning patterns from PHP applications

Monitoring Recommendations

• Enable Windows Security Event logging for process creation (Event ID 4688) with command line auditing
• Configure web application firewalls to detect and block file upload attempts targeting executable extensions
• Implement file integrity monitoring on application directories to detect unauthorized file additions
• Review Symfony application logs for unusual Process component usage patterns

How to Mitigate CVE-2024-51736

Immediate Actions Required

• Upgrade Symfony to patched versions: 5.4.46, 6.4.14, or 7.1.7 or later
• Audit application directories for presence of unexpected executable files
• Review file upload functionality to ensure proper validation and storage outside web-accessible directories
• Implement directory permissions that prevent writing executable files to application directories

Patch Information

Symfony has addressed this vulnerability in the following releases:

Users should upgrade to the appropriate fixed version for their branch. The security advisory is available at the Symfony GitHub Security Advisory.

Workarounds

• No official workarounds are available for this vulnerability according to the vendor advisory
• As a defense-in-depth measure, configure directory permissions to prevent writing executable files to application directories
• Consider implementing application-level controls to validate working directory contents before Process component usage
• Deploy endpoint protection that can detect and block execution of unsigned binaries from web application directories

# Verify Symfony version and upgrade
composer show symfony/process
composer require symfony/process:^5.4.46
# or for 6.x
composer require symfony/process:^6.4.14
# or for 7.x
composer require symfony/process:^7.1.7