CVE-2026-40296: PhpSpreadsheet has XSS via number format code with @ text placeholder bypasses htmlspecialchars in HTML writer

April 28, 2026 (updated May 8, 2026)

It was discovered that there is a way to bypass HTML escaping in the HTML writer using custom number format codes.

References

github.com/PHPOffice/PhpSpreadsheet
github.com/PHPOffice/PhpSpreadsheet/security/advisories/GHSA-hrmw-qprp-wgmc
github.com/advisories/GHSA-hrmw-qprp-wgmc
nvd.nist.gov/vuln/detail/CVE-2026-40296

Code Behaviors & Features

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