CVE-2026-35453: PhpSpreadsheet has XSS via NumberFormat @ Text Substitution in HTML Writer

April 28, 2026 (updated May 8, 2026)

The HTML Writer in PhpSpreadsheet bypasses htmlspecialchars() output escaping when a cell uses a custom number format containing the @ text placeholder with additional literal text (e.g., @ "items" or "Total: "@). This allows an attacker to inject arbitrary HTML and JavaScript into the generated HTML output by crafting a malicious XLSX file.

References

github.com/PHPOffice/PhpSpreadsheet
github.com/PHPOffice/PhpSpreadsheet/security/advisories/GHSA-6wpp-88cp-7q68
github.com/advisories/GHSA-6wpp-88cp-7q68
nvd.nist.gov/vuln/detail/CVE-2026-35453

Code Behaviors & Features

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