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CVE-2026-40296

5.4 · MEDIUM

PhpSpreadsheet is a pure PHP library for reading and writing spreadsheet files.

Published May 6, 2026CWE-79EPSS 0.25%

Overview

CVE-2026-40296 is a medium-severity vulnerability. 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, patches, and mitigation guidance. 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.

References

GitHubgithub.com/PHPOffice/PhpSpreadsheet/security/advisories/GHSA-hrmw-qprp-wgmcGitHubgithub.com/PHPOffice/PhpSpreadsheet/security/advisories/GHSA-hrmw-qprp-wgmc

How CyberStrike helps

Frequently asked questions

What is CVE-2026-40296?

CVE-2026-40296 is a medium-severity vulnerability. 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, patches, and mitigation guidance. 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 is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-40296 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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