Registry Keys are Keys to Your Network

Threat Hunting Scenario  “Registry Keys are Keys to Your Network”

This Blog focuses on a common lateral movement tactic involving the Windows Registry. Attackers can use registry modifications to establish persistence or elevate privileges. We’ll explore how to detect abnormal registry operations, particularly through the reg.exe command line tool.

Scenario Background

Use Case: Command Shell Invocation of Reg.exe
Tactic: Establishing Persistence
MITRE Reference: CAR-2013-03-001 (Reg.exe Called from Command Shell)

Legitimate registry changes typically occur through regedit.exe, the Registry APIs, or well-known administrative tools. However, reg.exe provides a command-line interface for querying and modifying the registry, often executed from a shell like cmd.exe. This can be abused to insert malicious startup items, disable security controls, or perform privilege escalations.

Key Observations

• Common Parent Process: When initiated by a user, these actions typically show cmd.exe as the parent process and, further up the tree, explorer.exe.
• Power Users/Administrators: In some environments, advanced users employ scripts for registry operations. These legitimate tasks often have recognizable process trees or are run from known administrative scripts.
• Filtering Legitimate Traffic: Reducing false positives is vital. It’s important to filter out known, scheduled scripts or IT automation tasks.

Real-World Example

In one notable breach at a large financial institution, attackers gained initial access via phishing. After establishing a foothold, they used reg.exe to create a malicious “Run” key in the Windows Registry. This key ensured a trojan would automatically start each time the system rebooted.

1. Phishing Email: The user unknowingly executed malware that provided initial access.
2. Registry Modification: Attackers launched cmd.exe under the context of the compromised user, then used reg.exe to insert a new startup entry in HKCU\Software\Microsoft\Windows\CurrentVersion\Run.
3. Persistence Achieved: Once the user logged back in, the malware relaunched, allowing attackers to maintain a continuous presence while avoiding detection by some endpoint solutions that only scanned on system startup.

Detection Strategy

1. Event Log Analysis: Use Windows Event Logs (Event ID 4688 for process creation) to monitor for reg.exe activity, capturing parent-child relationships.
2. Process Tree Tracking: Tools like EDR can build process trees and identify unusual parent processes for reg.exe.
3. Behavioral Baselines: Establish what normal registry modifications look like in your environment. Alert on deviations or suspicious parameters like -s (silent) or references to unfamiliar registry paths.