Gootloader Identified at Legal Services Firms in Drive-By Attacks

Adversaries don’t work 9-5 and neither do we. At eSentire, our 24/7 SOCs are staffed with Elite Threat Hunters and Cyber Analysts who hunt, investigate, contain and respond to threats within minutes.

We have discovered some of the most dangerous threats and nation state attacks in our space – including the Kaseya MSP breach and the more_eggs malware.

Our Security Operations Centers are supported with Threat Intelligence, Tactical Threat Response and Advanced Threat Analytics driven by our Threat Response Unit – the TRU team.

In TRU Positives, eSentire’s Threat Response Unit (TRU) provides a summary of a recent threat investigation. We outline how we responded to the confirmed threat and what recommendations we have going forward.

Here’s the latest from our TRU Team…

What did we find?

• Gootloader, a drive-by social engineering threat, delivered using poisoned search results. It acts as a precursor to threats such as Gootkit RAT, Cobalt Strike, REvil ransomware, and others.
• eSentire teams responded to multiple incidents at legal services customers and in all cases, the victim had searched for document templates including the keyword “agreement”.
• Search results led to websites that injected a fake forum overlay presenting the requested document, consistent with previous Gootloader attacks.
• Instead of a legitimate document, the victim is lured into downloading a zip archive containing a JavaScript file. When opened, the file is executed by Windows script host (wscript), resulting in PowerShell execution on the device.

Figure 1: Infection Process

How did we find it?

• BlueSteel, our machine-learning powered PowerShell classifier, identified PowerShell commands executed by Gootloader.
• An additional incident was identified through threat hunting activity.

What did we do?

• Our team of 24/7 SOC Cyber Analysts isolated the host and worked with the customer to remediate the threat.

What can you learn from this TRU positive?

• Gootloader is drive-by social engineering threat not unlike threats such as Solarmarker. These attacks don’t rely on software-level exploits, but trick victims into executing code disguised as office documents.
• Gootloader targets search phrases containing the keyword “agreement”, a common term used in the legal services field and likely to be found in document names.
• Employees who commonly seek out internet-hosted documents or document templates are more likely to stumble upon poisoned search results.
• Legal services customers have accounted for 70% of all Gootloader cases actioned by our SOC in 2021.

Recommendations from our Threat Response Unit (TRU) Team:

1. A security-aware workforce is a good first line of defense but may not be enough. Compensating controls focused on common code execution techniques (such as script files executed by unwitting users) is recommended.
2. Display file extensions for known file types.
3. Make sure you trust document sources. Even legitimate Word and Excel documents from the Internet can lead to malware.
4. Use Windows Attack Surface Reduction rules to block JavaScript and VBScript form launching downloaded content. Read more on Microsoft Docs.
5. Employ an Endpoint Detection and Response (EDR) tool to detect and isolate threats before they spread laterally.
6. Phishing and security awareness training should be mandated for all company employees. The training should focus on the following topics:
• The downloading and execution of files from unverified sources.
• Process for reporting potential security incidents.
• Educate users about safe Internet browsing habits.
• Avoid free versions of paid software.
• Inspect the full URL before downloading files to ensure it matches the source (e.g., Microsoft Teams should come from a Microsoft domain).
• Always inspect the extension of files, do not trust the filetype logo alone. An executable file can be disguised as a PDF or office document.
• Employees need to report security threats without fear of repercussion, even if caused accidentally.

Ask Yourself...

• Do your users commonly interact with internet-sourced documents?
• Do you have protections in place to identify and contain executable content disguised as office documents?

Indicators of Compromise

If you’re not currently engaged with a Managed Detection and Response provider, we highly recommend you partner with us for security services in order to disrupt threats before they impact your business.

Want to learn more? Connect with an eSentire Security Specialist