Updated May 2021

Antivirus (AV) is one of the most fundamental tools that an organization can deploy to provide security to their organization.  A typical antivirus solution primarily uses signature–based detections for identifying threats on a system which may not catch the most advanced threats, but it is still helpful in detecting some commodity malware and hacking tools. Despite antivirus falling short to more modern endpoint detection and response (EDR) solutions, it is a useful resource for an organization to leverage for threat hunting. 

Due to the overwhelming number of security service tools in any one environment, it is common for security teams to focus only on actionable detections and possibly overlook those that were mitigated by the security tool, as well as low severity detections. However, these detections can sometimes be an early warning sign of a significant threat. 

While there are many trivial methods to armor a malicious file against AV detection, occasionally some malware and tools get caught. Attackers typically have a backup plan though, and will either alter and recompile the malware again, or use a different tool or technique and continue on with the task at hand. In fact, during an investigation it is not uncommon to find malware detections on compromised hosts that were overlooked, either because the malware was quarantined, or had a lower severity or generic signature. This demonstrates the need for a process to hunt through these less urgent detections. 

Additionally, AV logs can be a good place to identify risky applications and potentially unwanted software that may be present on user workstations. Although these files may not be a direct security threat, they may highlight weaknesses in enforcement policies or use of unapproved applications. 

As part of our Threat Hunting Use Case series, we’re sharing the use case below around antivirus and malware, developed and refined by our Research and Development teams, to help you get started threat hunting. While AV logs are not the most robust log source for threat hunting, they are a useful resource for a threat hunter to sweep multiple endpoints throughout an enterprise, and quickly identify some low hanging fruit that could point to a larger threat, and possibly lead to more targeted hunting.  

Use Case: Antivirus & Malware

Objective: The objective of this threat hunt is to identify notable threats in order to increase effectiveness of AV logging and provide visibility into trends and coverage from your Antivirus solution. 

Log Source & Requirements: Anti-Virus, HIDS/HIPS 

Duration: 30-90 Days 

Related MITRE Techniques: T1203, T1059, T1562, T1566, T1204  

Outcomes: 

Baseline/Hygiene

What to look for  Why? 
Review detections for uncleaned threats to determine if any host groups should be configured with a higher enforcement level. Most AV solutions have the ability to adjust the sensitivity for specific groups of devices so critical hosts such as servers can be set with a higher level of protection. Reviewing the action taken on detected files per group is a good way to evaluate their effectiveness and identify any potential sensitivity changes needed. 
Look for detections related to risky software or potentially unwanted programs (PUP) to identify unapproved software on hosts in the environment. Detections such as these might highlight applications that may not be inherently malicious activity, (an indicator of compromise (IOC)) but could be abused for malicious purposes or could possibly be a privacy risk. 

 

Threat Analysis

What to look for Why?
Identify signatures and files with the least frequency of occurrence.  Truly malicious files or activity should be rare across endpoints in the environment. Reviewing the most infrequent detections is a great way to quickly highlight more serious threats. 
Look for files located in privileged directories (C:\, C:\Windows, C:\Windows\System32, etc.) or remote file paths (\\host). Suspicious files found in privileged directories could indicate a threat with elevated privileges. Files detected in a remote path were likely copied from another host, and could be an indicator of lateral movement. 
Hunt for malware hiding in plain sight by looking for common windows processes names that are misspelled (scvhost.exe) or located in the wrong directory (c:\windows\svchost.exe). Hiding in plain sight is a common and often effective evasion technique in which malware attempts to blend in with legitimate files or activity. 
Hunt for signatures categorized as hacking tools, backdoors, remote access tools, or credential dumpers regardless of the action taken. Detections such as these should be considered high severity as they could indicate post exploit activity in which a threat actor is performing actions on a compromised host.  

Make threat hunting a reality at your organization with ReliaQuest GreyMatter.

By aggregating and normalizing your data sets from disparate tools, such as SIEM, EDR, multi-cloud, and third-party applications, ReliaQuest GreyMatter allows your team to run focused hunt campaigns, both packaged and freeform that are strategic and iterative. Use ReliaQuest GreyMatter to analyze indicators of compromise retrospectively or perform behavior assessments to visualize abnormal from normal activity.

Ready to kick start your threat hunting program? Get the white paper: Threat Hunting 101.

Check out the other blogs in our Threat Hunting Use Case Series: