How to Check a WordPress Theme for Malicious Code Before Installation

WordPress is one of the most popular platforms for building websites, but its popularity makes it a target for cyber threats. Installing a compromised WordPress theme can expose your site to vulnerabilities, malware, and unauthorized access. Before you install any WordPress theme—especially one from an untrusted or free source—it’s essential to check for malicious code to protect your website and data.

This guide will walk you through how to thoroughly inspect a WordPress theme for malicious code before installation, ensuring your site remains secure.

“IN TODAY’S WORLD, ENDPOINT PROTECTION IS NO LONGER A LUXURY; IT’S A NECESSITY. FAILING TO SECURE ENDPOINTS IS LIKE LEAVING THE FRONT DOOR OPEN FOR CYBERCRIMINALS, EXPOSING BUSINESSES TO THEFT, DISRUPTION, AND FINANCIAL LOSS.”

Raj Samani, Chief Scientist at McAfee

Why Check WordPress Themes for Malicious Code?

Malicious code embedded in WordPress themes can cause serious problems for your website, including:

• Data theft: Hackers may access sensitive information, such as user credentials or personal data.
• Site redirection: Visitors could be redirected to spammy or harmful websites.
• Search engine penalties: Google and other search engines may blacklist your site for hosting malware.
• Unauthorized access: Hackers might use backdoors in the theme to control your site.

Being proactive and checking for malicious code before installation can save you from headaches down the line.

Step 1: Only Download Themes from Trusted Sources

The first step in ensuring a secure WordPress theme is to obtain it from a reputable source. Trusted platforms include:

• WordPress.org Theme Directory: All themes in the official directory are reviewed for security and functionality.
• Premium Theme Providers: Companies like StudioPress, ThemeForest, and Elegant Themes offer high-quality themes with customer support.
• Developer Websites: If you trust a developer, downloading directly from their site can reduce risk.

Avoid downloading themes from random third-party websites offering “nulled” or “free premium themes.” These are often riddled with malicious code.

Step 2: Scan the Theme Files Using an Online Tool

Before uploading the theme to your WordPress site, use online scanning tools to detect any malicious code. Here are some reliable tools:

1. VirusTotal
   Upload the theme’s ZIP file to VirusTotal. This service scans the file using multiple antivirus engines to identify malware or suspicious behavior.
2. Theme Authenticity Checker (TAC)
   TAC is a WordPress plugin that scans installed themes for suspicious code. While you’ll need to install the theme for this plugin to work, you can use it on a test site to avoid compromising your live site.
3. Sucuri SiteCheck
   Sucuri offers a powerful online tool for detecting malware. Although it’s typically used for live websites, you can upload files for scanning in some cases.

Step 3: Manually Inspect the Theme Files

If you’re comfortable with a bit of technical work, manually inspect the theme files for suspicious code. Here’s how:

1. Extract the ZIP File
   Unzip the theme file on your computer to examine its contents.
2. Check for Unnecessary Files
   Look for unusual files or folders, such as:
   • README.txt files unrelated to the theme.
   • PHP files in unexpected directories.
   • Hidden files or folders (e.g., .htaccess or .htpasswd in the wrong locations).
3. Examine the Code
   Open the PHP files in a code editor like Visual Studio Code or Notepad++ and search for:
   • base64_decode: This function is often used to obfuscate malicious code. While not inherently bad, excessive use is a red flag.
   • eval(): This function executes arbitrary PHP code, making it a favorite tool for hackers.
   • Suspicious URLs: Look for unfamiliar URLs or domains hardcoded into the theme files.
   • Encrypted Code: Any code that looks scrambled or unreadable might be malicious.
4. Compare with Known Good Code
   If you’re unsure about a specific file, compare it to similar files in other themes you trust. For example, compare the functions.php file of the suspicious theme to that of a theme from the WordPress repository.

Step 4: Test the Theme in a Local Environment

Before deploying the theme on your live site, test it in a safe, local environment. Tools like Local by Flywheel or XAMPP let you create a WordPress site on your computer without risk to your production site.

1. Install the theme on the local site.
2. Observe how it behaves. Look for:
   • Unexpected pop-ups or redirections.
   • Slow performance or unusual resource usage.
   • Errors or warnings in your WordPress dashboard.

If you notice anything unusual, investigate further before installing the theme on your live site.

Step 5: Use a Security Plugin to Monitor Activity

Even after installation, you should continuously monitor your site for threats. Install a WordPress security plugin to detect and neutralize malicious activity. Popular options include:

1. Wordfence Security: Scans files for malicious code and monitors login attempts.
2. iThemes Security: Protects against brute force attacks and scans for malware.
3. Sucuri Security: Provides website firewalls and malware scanning.

These plugins can alert you to threats, even if you missed something during your initial inspection.

Step 6: Keep Your Themes Updated

Outdated themes can contain vulnerabilities that hackers exploit. Regularly check for updates and install them promptly. If a theme is no longer supported by its developer, consider switching to a more secure alternative.

Red Flags to Watch Out For

Here are some warning signs that a theme might contain malicious code:

• Nulled Themes: Avoid themes labeled as “free premium” or “nulled.” These are often tampered with to include malware.
• No Developer Information: If the theme lacks details about its developer or source, it may be unsafe.
• Bundled Plugins: Some themes include unnecessary plugins, which may be vectors for malicious code.
• Obfuscated Code: If parts of the theme code are encrypted or hard to read, it could hide malicious scripts.

Conclusion

Installing a WordPress theme is an exciting step in building your website, but taking shortcuts can compromise your site’s security. By following these steps, you can ensure your theme is free from malicious code and safe to use. Remember to always source themes from reputable providers, use scanning tools, and test them thoroughly before installation.

A little caution today can save you from major security headaches tomorrow. Stay vigilant, and your WordPress site will remain a secure and thriving platform for your online presence!