CVE-2026-40296
5.4 · MEDIUMOverview
CVE-2026-40296 is a medium-severity vulnerability affecting phpoffice phpspreadsheet. It was published on May 6, 2026 and has a CVSS 3.1 base score of 5.4 (MEDIUM).
This vulnerability has a CVSS 3.1 base score of 5.4, rated MEDIUM. It can be exploited remotely over the network. Some level of privileges is required for exploitation.
Technical Description
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.
Remediation
Check the references section for vendor advisories and patches from phpoffice. Update phpspreadsheet to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
Affected Products
| Vendor | Product | Versions | Status |
|---|---|---|---|
| phpoffice | phpspreadsheet | >= 0, < 1.30.4 | Affected |
Frequently Asked Questions
What is CVE-2026-40296?
CVE-2026-40296 is a medium-severity vulnerability affecting phpoffice phpspreadsheet. It was published on May 6, 2026 and has a CVSS 3.1 base score of 5.4 (MEDIUM).
How severe is CVE-2026-40296?
This vulnerability has a CVSS 3.1 base score of 5.4, rated MEDIUM. It can be exploited remotely over the network. Some level of privileges is required for exploitation.
How do I fix or remediate CVE-2026-40296?
Check the references section for vendor advisories and patches from phpoffice. Update phpspreadsheet to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
How can CyberStrike help with CVE-2026-40296?
CyberStrike's AI-powered security agents can automatically detect CVE-2026-40296 across your infrastructure using autonomous pentesting, DAST scanning, and HackBrowser. The platform continuously monitors for known vulnerabilities and provides actionable remediation guidance prioritized by real-world exploitability.
How CyberStrike Helps
AI agents map your attack surface to find vulnerabilities like this one.
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