Different threat-hunting hypotheses

Hypothesis 1: Persistence

An adversary is maintaining a persistent foothold by modifying Windows Registry Run keys on non-standard host systems (e.g., development servers).

Tools:

* Endpoint Detection and Response (EDR): Used to query all systems for specific registry key modifications (HKCU\Software\Microsoft\Windows\CurrentVersion\Run).

* OSQuery/Velociraptor: Used for rapid, ad-hoc, deep-dive querying of endpoint file systems and registry keys across the environment.

Technique: Stack Counting & Baselining—Search for all entries written to the Run key in the last 90 days, focusing on entries that execute files from unusual directories (e.g., user profiles, temporary folders) or processes without valid digital signatures.

Containment & Eradication:

1. Isolate the affected host(s) immediately from the network (network containment).

2. Delete the malicious registry key entry and the associated file/payload.

3. Full Forensic Image/Memory Dump of the host to determine initial access and lateral movement.

4. Update Detection: Create a high-fidelity detection rule (e.g., Sigma rule) to alert on any future modifications to this specific registry path by any non-whitelisted process.

Hypothesis 1: Persistence

An adversary is maintaining a persistent foothold by modifying Windows Registry Run keys on non-standard host systems (e.g., development servers).

Tools:

* Endpoint Detection and Response (EDR): Used to query all systems for specific registry key modifications (HKCU\Software\Microsoft\Windows\CurrentVersion\Run).

* OSQuery/Velociraptor: Used for rapid, ad-hoc, deep-dive querying of endpoint file systems and registry keys across the environment.

Technique: Stack Counting & Baselining—Search for all entries written to the Run key in the last 90 days, focusing on entries that execute files from unusual directories (e.g., user profiles, temporary folders) or processes without valid digital signatures.

Containment & Eradication:

1. Isolate the affected host(s) immediately from the network (network containment).

2. Delete the malicious registry key entry and the associated file/payload.

3. Full Forensic Image/Memory Dump of the host to determine initial access and lateral movement.

4. Update Detection: Create a high-fidelity detection rule (e.g., Sigma rule) to alert on any future modifications to this specific registry path by any non-whitelisted process.

Hypothesis 2: Command and Control (C2)

Compromised internal hosts are communicating with a Command and Control (C2) server via DNS Tunneling to bypass egress controls.

Tools:

* Network Detection and Response (NDR) / Zeek (formerly Bro): For deep packet inspection and detailed DNS logging.

* Security Information and Event Management (SIEM) / Splunk: For log aggregation and correlation.

Technique: Anomaly Detection & Statistical Analysis—Analyze DNS logs for: (a) unusually long DNS query strings (characteristic of tunneling), (b) high volume of DNS requests to a single external domain, and (c) requests occurring outside of business hours (Moustafa et al., 2021).

Containment & Mitigation:

1. Block the malicious external IP address and C2 domain at the firewall/DNS layer organization-wide.

2. Identify all hosts that communicated with the blocked domain.

3. Analyze the original process that initiated the suspicious DNS request on the affected endpoint.

4. Develop and Deploy updated Network Intrusion Detection System (NIDS) signatures to detect long-string DNS tunneling patterns.

Hypothesis 3: Lateral Movement

An adversary is exploiting Valid Accounts to move laterally by repeatedly running commands like whoami.exe or net.exe on multiple hosts in a short timeframe.

Tools:

* Security Information and Event Management (SIEM): To correlate Windows Event Log IDs (e.g., Event ID 4688: Process Creation/Execution logs).

* User and Entity Behavior Analytics (UEBA): To baseline and flag anomalous user login behavior.

Technique: Behavioral Analytics & Correlation—Query for the execution of administrative tools (net.exe, psexec.exe, Invoke-Expression) that originate from an interactive login session (Logon Type 2 or 10) but occur on three or more different endpoints within a 30-minute window by the same non-administrator user (Sutton et al., 2020).

Response & Account Compromise:

1. Immediate Password Reset and Forced Logout for the compromised user account.

2. Disable or revoke all remote access permissions (RDP/SSH) for the user until an investigation is complete.

3. Scrub all hosts the user accessed for any new persistence mechanisms (see Hypothesis 1).

4. Improve Multi-Factor Authentication (MFA) enforcement across all remote access points.

Hypothesis 4: Privilege Escalation

An attacker is attempting to escalate privileges by exploiting a common Living-Off-The-Land Binary (LOLBin), specifically using PowerShell with obfuscated, encoded commands.

Tools:

* EDR/System Logs: To collect and analyze PowerShell Script Block Logging and Command Line logs.

* SIEM/Detection Engine: To search for the argument string -EncodedCommand or -e within powershell.exe process execution logs.

Technique: String Searching and Decoding—Search all PowerShell execution logs for the presence of the base64-encoded command argument. Once identified, decode the command to determine the payload (e.g., downloading a second-stage dropper or running Mimikatz) (Moustafa et al., 2021).

Hardening & Prevention:

1. Kill the offending PowerShell process and isolate the host.

2. Block the specific command or script payload identified during decoding.

3. Implement Constrained Language Mode for PowerShell execution on all production endpoints to severely limit the functionality of PowerShell for non-approved uses.

4. Create a new detection rule to alert on all execution of PowerShell that exceeds a specific command-line length threshold, which often indicates encoding.