PhpSpreadsheet allows bypass XSS sanitizer using the javascript protocol and special characters
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)ResearchThe 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*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](https://github.com/user-attachments/assets/b9d53f7a-6f36-4853-95f9-8aa22f81eccd)*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*It's clear that the javascript protocol with special characters is used.![fig12](https://github.com/user-attachments/assets/7595e88b-9848-4251-845c-2c2d8032e479)*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*CreditThis vulnerability was discovered by **Aleksey Solovev (Positive Technologies)**