What is CVE-2026-40296?

CVE-2026-40296 is a medium-severity vulnerability in Phpoffice Phpspreadsheet, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2026-05-06.

How severe is CVE-2026-40296?

Medium severity. CVSS v3 base score is 5.4 out of 10.

XSS in Phpoffice Phpspreadsheet

CVE-2026-40296

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 containin…

Vulnerability class: XSS (Cross-Site Scripting)

EPSS: 0.000 (1.7th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N.

Affected products

Phpoffice Phpspreadsheet — versions >= 4.0.0, <= 5.6.0, >= 3.3.0, <= 3.10.4, >= 2.2.0, <= 2.4.4

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

security-advisories@github.com (x_refsource_CONFIRM, Exploit, Mitigation, Vendor Advisory)

Frequently asked questions

What is CVE-2026-40296?: CVE-2026-40296 is a medium-severity vulnerability in Phpoffice Phpspreadsheet, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2026-05-06.
How severe is CVE-2026-40296?: Medium severity. CVSS v3 base score is 5.4 out of 10.