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Medium, CVSS 5.4

PhpSpreadsheet has XSS via number format code with @ text placeholder bypasses htmlspecialchars in HTML writer

CVE-2026-40296GHSA-hrmw-qprp-wgmc

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (phpoffice/phpspreadsheet 5.7.0, 3.10.5, 2.4.5, 2.1.16, 1.30.4), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • Packagist phpoffice/phpspreadsheet

    Affected
    >= 4.0.0, <= 5.6.0>= 3.3.0, <= 3.10.4>= 2.2.0, <= 2.4.4>= 2.0.0, <= 2.1.15<= 1.30.3
    Fixed in
    2.4.5, 1.30.4, 3.10.5, 2.1.16, 5.7.0

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
5.4 · CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
EPSS
  • CVE-2026-40296: 0.22% estimated exploitation activity in the next 30 days; percentile 13.24 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

It was discovered that there is a way to bypass HTML escaping in the HTML writer using custom number format codes. The Problem In Writer/Html.php around line 1592, the code checks if the formatted cell data equals the original data to decide whether to apply htmlspecialchars(): When a cell has a custom number format containing @ (text placeholder) with any additional literal characters, the formatter replaces @ with the cell value and adds the extra characters. This makes $cellData !== $origData, so htmlspecialchars() is skipped entirely. Even a single trailing space in the format (@ ) is enough to bypass the escape. Proof of Concept The generated HTML contains: The XSS payload is completely unescaped. Tested Bypass Formats | Format Code | Result | Escaped? | |---|---|---| | General (default) | Original value | YES (safe) | | . @ | . + value | NO (XSS!) | | @ (trailing space) | value + | NO (XSS!) | | x@ | x + value | NO (XSS!) | This was tested with PhpSpreadsheet 4.5.0 and…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 1 · created ·

    Published from ghsa record GHSA-hrmw-qprp-wgmc

Agent brief

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# Patch Next advisory brief: CVE-2026-40296

Advisory: PhpSpreadsheet has XSS via number format code with @ text placeholder bypasses htmlspecialchars in HTML writer
IDs: CVE-2026-40296, GHSA-hrmw-qprp-wgmc
Record: https://patchnext.com/advisories/cve-2026-40296 (revision 1, source checked 26 Oct 2026, 14:40 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: phpoffice/phpspreadsheet 5.7.0, 3.10.5, 2.4.5, 2.1.16, 1.30.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist phpoffice/phpspreadsheet: affected >= 4.0.0, <= 5.6.0; >= 3.3.0, <= 3.10.4; >= 2.2.0, <= 2.4.4; >= 2.0.0, <= 2.1.15; <= 1.30.3; fixed in 2.4.5, 1.30.4, 3.10.5, 2.1.16, 5.7.0

## Suggested inspection (read-only)
- Packagist phpoffice/phpspreadsheet: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on phpoffice/phpspreadsheet.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-hrmw-qprp-wgmc (GitHub-reviewed advisory GHSA-hrmw-qprp-wgmc lists affected ranges: Packagist phpoffice/phpspreadsheet >=4.0.0 =3.3.0 =2.2.0 =2.0.0 =0 <=1.30.3)

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