Kimai has an XXE Leading to Local File Read

Summary

### Summary Kimai uses [PHPSpreadsheet](https://github.com/PHPOffice/PhpSpreadsheet) for importing and exporting invoices. Recently, a [CVE](https://github.com/PHPOffice/PhpSpreadsheet/security/advisories/GHSA-ghg6-32f9-2jp7) was identified in PHPSpreadsheet, which could lead to an XXE vulnerability.

### Details

Exploitation requires an Administrator account, allowing the upload of an `XLSX` template containing the payload. The vulnerability is triggered by the following code snippet:

```php // https://github.com/kimai/kimai/blob/b1903ba18359be16dd32ea9c40377c486498f082/src/Invoice/Renderer/AbstractSpreadsheetRenderer.php#L41 public function render(InvoiceDocument $document, InvoiceModel $model): Response { $spreadsheet = IOFactory::load($document->getFilename()); $worksheet = $spreadsheet->getActiveSheet(); $entries = $model->getCalculator()->getEntries(); $sheetReplacer = $model->toArray(); $invoiceItemCount = \count($entries); if ($invoiceItemCount > 1) { $this->addTemplateRows($worksheet, $invoiceItemCount); } } ```

The `IOFactory::load` function utilizes `simplexml_load_string`, which has previously been demonstrated to be vulnerable to XXE attacks.

While this is not directly an XXE in Kimai, it does however impact the latest stable version.

### PoC

By uploading a malicious `XLSX` template, the payload will be triggered every time an invoice is generated.

```xml <?xml version="1.0" encoding='UTF-7' standalone="yes"?> +ADw-!DOCTYPE foo [ <!ENTITY % xxe SYSTEM "php://filter/......." > %xxe;]>..... ```

For a better a visibility, I will upload both a: - Malicious template sample for testing - An exported invoice, showing the contents of target file during the export.

### Impact Local File Read / RCE in edge cases where `phar://` can be utilized with [gadget chains](https://github.com/ambionics/phpggc) .

[export.xlsx](https://github.com/user-attachments/files/16803913/export.xlsx) [sample_template.xlsx](https://github.com/user-attachments/files/16803916/sample_template.xlsx)