How to Limit File Upload Formats in PHP

Cloudmersive
4 min readMay 7, 2024

File upload security is critical these days, and limiting file formats in our PHP form upload is a sensible security measure.

There are a few different ways we can specifically limit file upload formats in our PHP form (i.e., using built-in functions), but in this article, we’re going to highlight a free security API that allows us to perform a few different useful actions simultaneously.

This API will allow us to restrict file formats using a comma-separated list of acceptable file extensions (i.e., ‘.pdf,.png,.jpg,.jpeg’), and it’ll also scan each file for viruses and malware by referencing a continuously updated list of 17 million+ virus and malware signatures.

Additionally, this API will perform a deterministic threat scan on each files’ contents, ensuring potentially malicious content (such as macros, scripts, executables, etc.) are identified in the API response.

We can structure our API call in a few quick steps using ready-to-run PHP code examples. We can also authorize our API calls for free with a free Cloudmersive API key (this allows a limit of 800 API calls per month with no commitments).

Let’s start by installing the PHP client with Composer:

composer require cloudmersive/cloudmersive_virusscan_api_client

After that, let’s copy the below code to call the function. We can set Booleans to block a variety of threatening file types, and we can supply our comma-separated list of acceptable file extensions in the $restrict_file_types parameter:

<?php
require_once(__DIR__ . '/vendor/autoload.php');

// Configure API key authorization: Apikey
$config = Swagger\Client\Configuration::getDefaultConfiguration()->setApiKey('Apikey', 'YOUR_API_KEY');



$apiInstance = new Swagger\Client\Api\ScanApi(


new GuzzleHttp\Client(),
$config
);
$input_file = "/path/to/inputfile"; // \SplFileObject | Input file to perform the operation on.
$allow_executables = true; // bool | Set to false to block executable files (program code) from being allowed in the input file. Default is false (recommended).
$allow_invalid_files = true; // bool | Set to false to block invalid files, such as a PDF file that is not really a valid PDF file, or a Word Document that is not a valid Word Document. Default is false (recommended).
$allow_scripts = true; // bool | Set to false to block script files, such as a PHP files, Python scripts, and other malicious content or security threats that can be embedded in the file. Set to true to allow these file types. Default is false (recommended).
$allow_password_protected_files = true; // bool | Set to false to block password protected and encrypted files, such as encrypted zip and rar files, and other files that seek to circumvent scanning through passwords. Set to true to allow these file types. Default is false (recommended).
$allow_macros = true; // bool | Set to false to block macros and other threats embedded in document files, such as Word, Excel and PowerPoint embedded Macros, and other files that contain embedded content threats. Set to true to allow these file types. Default is false (recommended).
$allow_xml_external_entities = true; // bool | Set to false to block XML External Entities and other threats embedded in XML files, and other files that contain embedded content threats. Set to true to allow these file types. Default is false (recommended).
$allow_insecure_deserialization = true; // bool | Set to false to block Insecure Deserialization and other threats embedded in JSON and other object serialization files, and other files that contain embedded content threats. Set to true to allow these file types. Default is false (recommended).
$allow_html = true; // bool | Set to false to block HTML input in the top level file; HTML can contain XSS, scripts, local file accesses and other threats. Set to true to allow these file types. Default is false (recommended) [for API keys created prior to the release of this feature default is true for backward compatability].
$restrict_file_types = "restrict_file_types_example"; // string | Specify a restricted set of file formats to allow as clean as a comma-separated list of file formats, such as .pdf,.docx,.png would allow only PDF, PNG and Word document files. All files must pass content verification against this list of file formats, if they do not, then the result will be returned as CleanResult=false. Set restrictFileTypes parameter to null or empty string to disable; default is disabled.

try {
$result = $apiInstance->scanFileAdvanced($input_file, $allow_executables, $allow_invalid_files, $allow_scripts, $allow_password_protected_files, $allow_macros, $allow_xml_external_entities, $allow_insecure_deserialization, $allow_html, $restrict_file_types);
print_r($result);
} catch (Exception $e) {
echo 'Exception when calling ScanApi->scanFileAdvanced: ', $e->getMessage(), PHP_EOL;
}
?>

Now we can restrict file formats in our PHP form AND check files for threats simultaneously!

--

--

Cloudmersive

There’s an API for that. Cloudmersive is a leader in Highly Scalable Cloud APIs.