"CVE-2024-1874: Insufficient Escaping in PHP proc_open() Command Leading to Arbitrary Command Execution on Windows"

CVE-2024-1874 is a vulnerability existing in multiple versions of PHP: 8.1.* before 8.1.28, 8.2.* before 8.2.18, and 8.3.* before 8.3.5. The vulnerability is present when using the proc_open() command with the array syntax in Windows systems. Due to insufficient escaping of the user-supplied arguments, a malicious user can exploit this vulnerability to execute arbitrary commands in the Windows shell.

In this post, we'll discuss the details of this vulnerability, provide a code snippet demonstrating the issue, and give some recommendations for getting protected against it.

A typical usage of proc_open() with the array syntax may look like the following

$command = 'dir';
$args = ['*.txt'];
$descriptorspec = array(
     => array('pipe', 'r'),
    1 => array('pipe', 'w'),
    2 => array('pipe', 'w')
);
$pipes = [];
$process = proc_open($command, $descriptorspec, $pipes, NULL, $args);

In this example, the dir command goes through and lists all txt files in the current directory. This code demonstrates how proc_open() passes arguments to the command through the $args variable.

However, if a malicious user can control the $args value, they can execute arbitrary commands like this:

$command = 'dir';
$args = ['*.txt && echo "Malicious Command Executed"'];
$descriptorspec = array(
     => array('pipe', 'r'),
    1 => array('pipe', 'w'),
    2 => array('pipe', 'w')
);
$pipes = [];
$process = proc_open($command, $descriptorspec, $pipes, NULL, $args);

In this case, the user controls $args and adds their own command (echo "Malicious Command Executed"). Since the proc_open() function doesn't properly escape the user-submitted input, this command is executed along with the original one.

You can find more information regarding this vulnerability in the official references

- PHP Changelog
- MITRE Entry
- National Vulnerability Database

Exploit Details

An exploitation of this vulnerability requires the attacker to have control over the arguments passed to the proc_open() function. Some scenarios in which this may happen are:

The web application takes user input as part of the proc_open() command's arguments.

2. Another component of the software, such as a plug-in or third-party library, allows user input to leak into the arguments of the proc_open() function.

In order to exploit this vulnerability, a malicious user must provide specific, specially crafted input designed to break out of the context of the original command and inject additional commands.

* 8.3.5 or higher (For the 8.3.x series)

2. Always validate and sanitize user-provided inputs that are passed as arguments to proc_open() or other functions that execute system commands.
3. Limit the scope and permissions of the user running your PHP application to minimize potential impact in case of a successful exploit.

Conclusion

CVE-2024-1874 highlights the importance of properly handling user input when using functions like proc_open() in PHP. By updating to the latest PHP versions and implementing security best practices, you can help ensure the protection of your applications and users against such vulnerabilities.

Timeline

Published on: 04/29/2024 04:15:07 UTC
Last modified on: 05/01/2024 17:15:28 UTC