PhpSpreadsheet XSS via number format text substitution in HTML Writer

Summary

PhpSpreadsheet is a library for reading and writing spreadsheet files. In versions 1.30.3 and earlier, 2.0.0 through 2.1.15, 2.2.0 through 2.4.4, 3.3.0 through 3.10.4, and 4.0.0 through 5.6.0, the HTML Writer skips htmlspecialchars() output escaping when a cell uses a custom number format containing the @ text placeholder with additional literal text (e.g., @ "items"). The escaping is only applied when the formatted output strictly equals the original cell value. When the format code contains @ with quoted literal text, the formatter substitutes the raw cell value into the format string and returns early without invoking the escaping callback. An attacker who can control cell content in a spreadsheet processed by the HTML Writer can inject arbitrary HTML and JavaScript into the generated output. This issue has been fixed in versions 1.30.4, 2.1.16, 2.4.5, 3.10.5, and 5.7.0.

Timeline

1. May 5, 2026, 7:39 PM UTCCVE published
2. May 6, 2026, 2:27 PM UTCCISA SSVC assessment

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

3. May 6, 2026, 2:27 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