Excel.XLL Add-Ins Cause 600% Rise in Phishing Attacks: Stay Safe

Cybercriminals are using Excel .XLL add-ins in phishing campaigns more than ever before. In fact, the use of malicious Excel .XLL files has jumped by an incredible 588% in a short time, showing how attackers are finding new ways to bypass security defenses.

According to IBM's 2024 X-Force Threat Intelligence Index, nearly 85% of attacks on key industries start with methods like phishing emails, exploiting public websites, or using stolen login details. These numbers make it clear that cyber threats are getting smarter, and businesses must improve their defenses to stay protected.

In this blog, we’ll explain what Excel .XLL add-ins are, how attackers use them, why they’re so dangerous, and the best ways to keep your organization safe.

What Are Excel .XLL Add-Ins?

Excel .XLL add-ins are files designed to extend the functionality of Microsoft Excel. These dynamic link library (DLL) files allow developers to create custom tools, automate tasks, and enhance productivity.

However, the same features that make Excel.XLL files useful for legitimate purposes also make them a powerful tool for cybercriminals. These files are easy to deploy and can run malicious code when installed, making them ideal for phishing attacks.

How Are Excel .XLL Add-Ins Used in Phishing Attacks?

Attackers typically send phishing emails with Excel.XLL file attachments. These emails often trick users into opening the file and installing the add-in, which then deploys malware onto their system.

Malware such as Dridex, IcedID, BazaLoader, and Agent Tesla has been linked to Excel.XLL-based phishing campaigns. These attacks exploit the unique properties of Excel.XLL files, like their ability to run hidden code, which helps them bypass traditional antivirus tools and other security measures.

Why Are Excel. XLL-Based Attacks So Effective?

The unique characteristics of Excel.XLL files give attackers several advantages over traditional methods, making them a preferred tool for phishing campaigns.

• Advanced Functionality: Compared to VBA macros, Excel.XLL files can execute more complex tasks, making them an attractive option for attackers.
• Low Awareness: Many users are unfamiliar with Excel.XLL files, making them more likely to trust and open them.
• Cross-Platform Compatibility: Excel.XLL add-ins work on Windows, Mac, and web browsers, giving attackers more opportunities to target their victims.

These factors make Excel.XLL-based attacks not only effective but also difficult to detect with standard security solutions.

Real-World Impact

In 2021, cybercriminals used malicious Excel.XLL files to deliver the Dridex banking Trojan, targeting victims through phishing emails. Once users opened the Excel.XLL files, Dridex was installed on their systems, allowing attackers to steal banking credentials and sensitive information.

This attack caused significant financial losses and reputational damage for several organizations, highlighting the devastating impact of Excel.XLL-based threats. It serves as a critical reminder for businesses to bolster their defenses against such sophisticated tactics.

Recommendations to Protect Against Excel.XLL Phishing Attacks

To combat Excel.XLL-based phishing attacks, organizations must adopt both technical safeguards and employee training. Let’s dive into the key steps to strengthen your defenses.

1. Block Excel.XLL Attachments

Configure your email systems to block emails containing Excel.XLL files. This proactive step prevents malicious files from reaching employees, reducing the likelihood of accidental installation. It’s a crucial line of defense in stopping threats before they even enter your organization.

2. Restrict Add-In Permissions

Within Microsoft Excel, limit the permissions for add-ins to only those from trusted and verified sources. By restricting access, you minimize the risk of malicious add-ins being executed, protecting your systems from unauthorized scripts and malware.

3. Disable Unverified Add-Ins

Prevent the installation of unverified or custom Excel.XLL add-ins unless explicitly approved by your IT department. Enforcing this policy ensures that only safe and necessary add-ins are allowed, significantly lowering the risk of exploitation.

4. Train Employees

Provide employees with comprehensive security awareness training to help them recognize phishing emails and suspicious file types, including Excel.XLL files. Teach staff to treat unexpected attachments with caution and adopt a “verify-before-opening” approach to avoid falling victim to attacks.

5. Strengthen Endpoint Security

Ensure that all endpoint protection and antivirus software is regularly updated to detect and block the latest malware threats, including those delivered via Excel.XLL files. Modern antivirus solutions are essential for identifying hidden threats that exploit new vulnerabilities.

6. Use Multi-Factor Authentication (MFA)

Implement MFA to secure user accounts, adding an extra layer of protection against credential theft. Even if attackers gain access to a password, MFA prevents unauthorized access to sensitive systems and data.

7. Simulate Phishing Attacks

Test employee readiness using phishing simulations with tools like Keepnet Phishing Simulator. Simulations provide hands-on training, helping employees identify and respond to phishing attempts in a controlled environment, ultimately improving their real-world resilience.

Enhance Your Defense with Keepnet Solutions

The growing threat of Excel.XLL-based attacks requires more than just technical solutions—it demands a well-rounded strategy that includes employee training and real-world simulations.

• Keepnet Security Awareness Training: Educate employees on recognizing phishing attempts and malicious attachments.
• Keepnet Phishing Simulator: Test your team's readiness to handle phishing emails in a controlled environment.
• Keepnet Human Risk Management Platform: Benchmark your organization’s human risk score and take steps to improve it.