GHSA-q9jv-mm3r-j47r PhpSpreadsheet allows bypass XSS sanitizer using the javascript protocol and special characters

• Packagist phpoffice/phpspreadsheet: >= 3.0.0, < 3.7.0 → fixed in 3.7.0 • Packagist phpoffice/phpspreadsheet: < 1.29.7 → fixed in 1.29.7 • Packagist phpoffice/phpspreadsheet: >= 2.0.0, < 2.1.6 → fixed in 2.1.6 • Packagist phpoffice/phpspreadsheet: >= 2.2.0, < 2.3.5 → fixed in 2.3.5 • Packagist phpoffice/phpexcel: <= 1.8.2 (no fix yet)

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* ``` 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. *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&#x09;ascript:alert() jav&#x0D;ascript:alert() jav&#x0A;ascript:alert() ``` It's clear that the javascript protocol with special characters is used. *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. *Figure 13. Executing arbitrary JavaScript code* Credit This vulnerability was discovered by Aleksey Solovev (Positive Technologies)