How to Block HTML Input in your File Upload Process using Java

If uploads contain HTML input in the top level of a file, your system might be at risk of XSS (cross-site scripting), malicious scripts, or local file access attempts perpetrated by a client-side threat actor. It’s essential to actively enforce file upload security policies against such threats, or you risk allowing bad actors to easily compromise your system.

Thankfully, blocking HTML threats within file uploads is rather straightforward when you deploy a 360-degree content protection/verification API. The free-to-use API provided in this article allows you to scan files for millions of virus and malware threats and set policies against HTML inputs (and scripts) detected within any file’s contents.

To take advantage of this API in Java, simply copy & paste code examples provided below and you’ll be up and running within minutes.

First, let’s install the client SDK using Maven. Let’s add a reference to the repository in pom.xml:

<repositories>
    <repository>
        <id>jitpack.io</id>
        <url>https://jitpack.io</url>
    </repository>
</repositories>

Next, let’s add a reference to the dependency in pom.xml:

<dependencies>
<dependency>
    <groupId>com.github.Cloudmersive</groupId>
    <artifactId>Cloudmersive.APIClient.Java</artifactId>
    <version>v4.25</version>
</dependency>
</dependencies>

With installation out of the way, let’s now structure our API call using the ready-to-run code examples below:

// Import classes:
//import com.cloudmersive.client.invoker.ApiClient;
//import com.cloudmersive.client.invoker.ApiException;
//import com.cloudmersive.client.invoker.Configuration;
//import com.cloudmersive.client.invoker.auth.*;
//import com.cloudmersive.client.ScanApi;

ApiClient defaultClient = Configuration.getDefaultApiClient();

// Configure API key authorization: Apikey
ApiKeyAuth Apikey = (ApiKeyAuth) defaultClient.getAuthentication("Apikey");
Apikey.setApiKey("YOUR API KEY");
// Uncomment the following line to set a prefix for the API key, e.g. "Token" (defaults to null)
//Apikey.setApiKeyPrefix("Token");

ScanApi apiInstance = new ScanApi();
File inputFile = new File("/path/to/inputfile"); // File | Input file to perform the operation on.
Boolean allowExecutables = true; // Boolean | Set to false to block executable files (program code) from being allowed in the input file.  Default is false (recommended).
Boolean allowInvalidFiles = true; // Boolean | 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).
Boolean allowScripts = true; // Boolean | 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).
Boolean allowPasswordProtectedFiles = true; // Boolean | 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).
Boolean allowMacros = true; // Boolean | 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).
Boolean allowXmlExternalEntities = true; // Boolean | 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).
Boolean allowInsecureDeserialization = true; // Boolean | 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).
Boolean allowHtml = true; // Boolean | 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].
String restrictFileTypes = "restrictFileTypes_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 {
    VirusScanAdvancedResult result = apiInstance.scanFileAdvanced(inputFile, allowExecutables, allowInvalidFiles, allowScripts, allowPasswordProtectedFiles, allowMacros, allowXmlExternalEntities, allowInsecureDeserialization, allowHtml, restrictFileTypes);
    System.out.println(result);
} catch (ApiException e) {
    System.err.println("Exception when calling ScanApi#scanFileAdvanced");
    e.printStackTrace();
}

To authenticate your request for free, simply copy in your free-tier API key (this comes with a limit of 800 API calls per month and no commitments). After that, set the allowHtml boolean to “false” to categorically block all HTML code found within file uploads, and set allowScripts to “false” to block additional embedded threats.

It’s just that easy — now you have a powerful security policy in place against a multitude of file upload threats.