PhpSpreadsheet vulnerable to XSS in HTML writer via custom number format codes

Summary

PhpSpreadsheet is a pure PHP library for reading and writing spreadsheet files. The HTML writer skips htmlspecialchars escaping when a cell's formatted value differs from the original value. When a cell has a custom number format containing the text placeholder @ along with any additional literal characters (for example ". @", "@ ", or "x@"), the formatter replaces @ with the cell value and adds the extra characters, causing the formatted value to differ from the original and bypassing HTML escaping entirely. An attacker who can control the cell value and number format of an uploaded spreadsheet that is later converted to HTML and displayed to other users can achieve stored cross-site scripting. This issue is fixed in versions 5.7.0, 3.10.5, 2.4.5, 2.1.16, and 1.30.4.

Timeline

1. May 6, 2026, 8:48 PM UTCCVE published
2. May 7, 2026, 2:02 PM UTCCISA SSVC assessment

   Exploitation: poc · Automatable: no · Technical impact: partial

3. May 7, 2026, 2:03 PM UTCRecord last updated

Affected versions

• PHPOffice PhpSpreadsheet

  From 4.0.0 · through 5.6.0; From 3.3.0 · through 3.10.4; From 2.2.0 · through 2.4.4; From 2.0.0 · through 2.1.15; through 1.30.3

• phpoffice/phpspreadsheetPackagist

  From 4.0.0 · fixed in 5.7.0

• phpoffice/phpspreadsheetPackagist

  From 3.3.0 · fixed in 3.10.5

• phpoffice/phpspreadsheetPackagist

  From 2.2.0 · fixed in 2.4.5

• phpoffice/phpspreadsheetPackagist

  From 2.0.0 · fixed in 2.1.16

• phpoffice/phpspreadsheetPackagist

  fixed in 1.30.4

References 1