Cross-Site Scripting (XSS) vulnerability of the hyperlink base in the HTML page header
Product: Phpspreadsheet Version: version 3.6.0 CWE-ID: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') CVSS vector v.3.1: 5.4 (AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N) CVSS vector v.4.0: 4.8 (AV:N/AC:L/AT:N/PR:L/UI:A/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N) Description: the HTML page is formed without sanitizing the hyperlink base Impact: executing arbitrary JavaScript code in the browser Vulnerable component: class PhpOffice\PhpSpreadsheet\Writer\Html, method generateHTMLHeader Exploitation conditions: a user viewing a specially generated Excel file Mitigation: additional sanitization of special characters in a string Researcher: Aleksey Solovev (Positive Technologies)
Research
The researcher discovered zero-day vulnerability Cross-Site Scripting (XSS) vulnerability of the hyperlink base in the HTML page header in Phpspreadsheet. The following code is written on the server, which translates the XLSX file into a HTML representation and displays it in the response.
Listing 8. Source code on the server
<?php
require DIR . '/vendor/autoload.php';
$inputFileName = './doc/Book1.xlsx'; $spreadsheet = \PhpOffice\PhpSpreadsheet\IOFactory::load($inputFileName); $writer = new \PhpOffice\PhpSpreadsheet\Writer\Html($spreadsheet); print($writer->generateHTMLAll());
An attacker can embed a payload in a file property that will result in the execution of arbitrary JavaScript code. The Excel file is unpacked and a HyperlinkBase in the file is inserted into the docProps/app.xml file.
!fig14
Figure 14. Embedding the payload
After the changes were made, a new archive with the xlsx extension was created. At the moment of converting the xlsx file into the HTML representation, a property is obtained that participates in the formation of a string without sanitization.
!fig15
Figure 15. Generating the HTML page header using the HyperlinkBase property
After generating and displaying the HTML representation of the XLSX file, arbitrary JavaScript code will be executed. <img width="356" alt="fig16" src="https://github.com/user-attachments/assets/c3694661-31e3-4be8-9a86-6eb4dd4647b5" />
Figure 16. Executing arbitrary JavaScript code
Credit This vulnerability was discovered by Aleksey Solovev (Positive Technologies)
Bypass XSS sanitizer using the javascript protocol and special characters
Product: Phpspreadsheet Version: version 3.6.0 CWE-ID: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') CVSS vector v.3.1: 5.4 (AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N) CVSS vector v.4.0: 4.8 (AV:N/AC:L/AT:N/PR:L/UI:A/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N) Description: an attacker can use special characters, so that the library processes the javascript protocol with special characters and generates an HTML link Impact: executing arbitrary JavaScript code in the browser Vulnerable component: class PhpOffice\PhpSpreadsheet\Writer\Html, method generateRow Exploitation conditions: a user viewing a specially generated Excel file Mitigation: additional sanitization of special characters in a string Researcher: Aleksey Solovev (Positive Technologies)
Research
The researcher discovered zero-day vulnerability Bypass XSS sanitizer using the javascript protocol and special characters in Phpspreadsheet.
The following code is written on the server, which translates the XLSX file into a HTML representation and displays it in the response.
Listing 6. Source code on the server
<?php
require DIR . '/vendor/autoload.php';
$inputFileName = './doc/Book1.xlsx'; $spreadsheet = \PhpOffice\PhpSpreadsheet\IOFactory::load($inputFileName); $writer = new \PhpOffice\PhpSpreadsheet\Writer\Html($spreadsheet); print($writer->generateHTMLAll());
An attacker can use special characters so that this library processes the javascript protocol with special characters and generates a HTML link. The Excel file is unpacked and a hyperlink in the file is inserted into the xl/worksheets/sheet1.xml file.
!fig11
Figure 11. Using the javascript protocol with special characters
Some payloads help bypass the security system and carry out a XSS attack.
Listing 7. HTML form that demonstrates the exploitation of the XSS vulnerability
jav	ascript:alert() jav
ascript:alert() jav
ascript:alert()
It's clear that the javascript protocol with special characters is used.
!fig12
Figure 12. Using the javascript protocol with special characters
Due to the special characters, the execution stream ends up on line 1543, and the link is built in HTML form with the javascript protocol.
<img width="373" alt="fig13" src="https://github.com/user-attachments/assets/3ca0c3c6-daa9-4502-ad9e-b803f308fd26" />
Figure 13. Executing arbitrary JavaScript code
Credit This vulnerability was discovered by Aleksey Solovev (Positive Technologies)
Summary The researcher discovered zero-day vulnerability Cross-Site Scripting (XSS) vulnerability in the code which translates the XLSX file into a HTML representation and displays it in the response.
Details When generating the HTML from an xlsx file containing multiple sheets, a navigation menu is created. This menu includes the sheet names, which are not sanitized. As a result, an attacker can exploit this vulnerability to execute JavaScript code.
php // Construct HTML $html = '';
// Only if there are more than 1 sheets if (count($sheets) > 1) { // Loop all sheets $sheetId = 0;
$html .= '<ul class="navigation">' . PHPEOL;
foreach ($sheets as $sheet) { $html .= ' <li class="sheet' . $sheetId . '"><a href="#sheet' . $sheetId . '">' . $sheet->getTitle() . '</a></li>' . PHPEOL; ++$sheetId; }
$html .= '</ul>' . PHPEOL; }
PoC 1. Create an XLSX file with multiple sheets : !image
2. Generate the HTML content php <?php require DIR . '/vendor/autoload.php';
$inputFileName = 'payload.xlsx'; $spreadsheet = \PhpOffice\PhpSpreadsheet\IOFactory::load($inputFileName); $writer = new \PhpOffice\PhpSpreadsheet\Writer\Html($spreadsheet); $writer->writeAllSheets(); echo $writer->generateHTMLAll(); ?> 3. Enjoy !image
Impact
XSS can cause a variety of problems for the end user that range in severity from an annoyance to complete account compromise. Example of impacts :
- Disclosure of the user’s session cookie, allowing an attacker to hijack the user’s session and take over the account (Only if HttpOnly cookie's flag is set to false). - Redirecting the user to some other page or site (like phishing websites) - Modifying the content of the current page (add a fake login page that sends credentials to the attacker). - Automatically download malicious files. - Requests access to the victim geolocation / camera. - ...