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Medium, CVSS 5.3

PhpSpreadsheet has XSS via NumberFormat @ Text Substitution in HTML Writer

CVE-2026-35453GHSA-6wpp-88cp-7q68

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 4.0
5.3 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N · score source
EPSS
  • CVE-2026-35453: 0.20% estimated exploitation activity in the next 30 days; percentile 10.25 (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.

Summary The HTML Writer in PhpSpreadsheet bypasses htmlspecialchars() output escaping when a cell uses a custom number format containing the @ text placeholder with additional literal text (e.g., @ "items" or "Total: "@). This allows an attacker to inject arbitrary HTML and JavaScript into the generated HTML output by crafting a malicious XLSX file. Details 1. Conditional escaping in Html.php:1586-1594 htmlspecialchars() is only called when $cellData === $origData (strict comparison). If the formatted output differs from the original value in any way, escaping is skipped entirely. 2. Early return in Formatter.php:136-152 When the format code contains @ with additional literal text (e.g., @ "items"), the formatter substitutes the raw cell value into the format string and returns early — the formatColor callback (which would have applied htmlspecialchars) is never invoked. PoC test.php The produced output contains unescaped data. <img width="719" height="716" alt="Screenshot 2026-04-02…

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

    Published from ghsa record GHSA-6wpp-88cp-7q68

Agent brief

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# Patch Next advisory brief: CVE-2026-35453

Advisory: PhpSpreadsheet has XSS via NumberFormat @ Text Substitution in HTML Writer
IDs: CVE-2026-35453, GHSA-6wpp-88cp-7q68
Record: https://patchnext.com/advisories/cve-2026-35453 (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 5.3)
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-6wpp-88cp-7q68 (GitHub-reviewed advisory GHSA-6wpp-88cp-7q68 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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