How to Virus Scan Files and Block Unsafe Archives (i.e., Zip Bombs) in Java

While file threats containing virus and malware signatures tend to attract the most attention in the file security review process, unsafe archives — like the infamous Zip Bomb, for example — pose an equally significant threat. If overloaded zip files are mistakenly opened within a system, they can crash that system and cause Denial of Service (DoS), which badly hurts a company’s reputation and often results in a severe violation of their SLA.

The only way to detect unsafe archives in the file upload process is by deploying full content verification policies to identify the archive’s contents. Verifying file extensions and headers alone won’t get the job done, and neither will the most exhaustive virus and malware checks.

Thankfully, the free-to-use API provided below gives you the option to categorically block unsafe archives in the file upload process, and it also performs a valuable virus and malware check, referencing all content against a list of more than 17 million virus and malware signatures — including ransomware, trojans, spyware, and more. You can take advantage of this API in minutes with ready-to-run Java code examples.

We can start by instaling the Java SDK with Maven. Let’s add a reference to the pom.xml repository:

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

After that, let’s add another reference to the pom.xml dependency:

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

Now that installation is out of the way, we can structure our API call using the below code snippet. We’ll need to authenticate our request with a free-tier API key (you can get one — with a limit of 800 API calls per month & no commitments — on the Cloudmersive website) and then set the allowUnsafeArchives boolean to “false”.

// 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();
}

With these policies in place, any files containing viruses, malware or unsafe archive contents will receive a CleanResult: False Boolean in the API response body. You can now delete or quarantine a wide variety of threats in a single request.