PhpSpreadsheet has a Cross-Site Scripting (XSS) vulnerability in custom properties
Cross-Site Scripting (XSS) vulnerability in custom properties**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 generated without clearing custom properties
**Impact**: executing arbitrary JavaScript code in the browser
**Vulnerable component**: class `PhpOffice\PhpSpreadsheet\Writer\Html`, method `generateMeta`
**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 Cross-Site Scripting (XSS) vulnerability in custom properties 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 9. Source code on the server*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 custom property in the file is inserted into the `docProps/custom.xml` file.![fig17](https://github.com/user-attachments/assets/65453b48-bca5-4f5c-a683-315a7bb1ab1f)*Figure 17. Embedding the payload*After making the changes, a new archive with the xlsx extension was created. At the moment of converting the xlsx file into an HTML representation, a property is obtained that participates in the formation of a string without sanitization.![fig18](https://github.com/user-attachments/assets/e0f63bfb-d9e1-4c9d-a2a9-8a0a20406cdc)*Figure 18. Getting a custom property*When calling the static `generateMeta` method, you can see that the key of the custom property is displayed without sanitization.![fig19](https://github.com/user-attachments/assets/8c74e264-af68-4f62-8ac7-437e65884e86)*Figure 19. Getting a custom property*As a result, when viewing the excel file as the HTML representation, arbitrary JavaScript code will be executed.*Figure 20. Executing arbitrary JavaScript code*CreditThis vulnerability was discovered by **Aleksey Solovev (Positive Technologies)**