This case study presents a challenging real-world forensic investigation conducted for a client, a mid-sized IT services provider, where an attacker compromised internal systems using previously unknown vulnerabilities. The investigation relied solely on  open-source tools to analyze Windows OS artifacts, including event logs, registry modifications, file system activities, and process execution data. The investigation highlights how open-source toolsets were utilized diligently to tackle significant roadblocks and challenges.

Overview of the Incident

Background

The client approached us after incidents of unauthorized access resulted in data leaks, including sensitive client credentials. IT administrators noticed reduced system performance on their domain controller and detected multiple failed logins occurring at abnormal times of the night. Endpoint protection tools provided negligible forensic context as they lacked audit logging and detection capabilities beyond basic malware.

Challenges

1. Attacker Strategy:
   • The attacker leveraged living-off-the-land binaries (LotL) like PowerShell and task scheduler, making detection difficult.
   • Fileless malware utilized, leaving minimal disk-based artifacts.
2. Partial Log Coverage:
   • Critical event log backups were missing due to misconfiguration in the centralized logging system.
   • The attacker tampered with and deleted portions of the security logs on specific systems.
3. Multiple Attack Vectors:

Tactics included registry key modifications, malicious scheduled tasks, and credential dumping via Windows utilities.

Investigation Methodology

Phase 1: Identification and Evidence Preservation

1. Immediate Actions:
   • Isolated the compromised machines from the network to contain the attack.
   • Acquired forensic disk images and volatile memory images from suspicious endpoints using FTK Imager Lite and Magnet RAM Capture.
     
2. Opened Investigation Tools:
   • Used Autopsy for comprehensive disk analysis.
   • Deployed Redline for volatile memory evidence extraction.

Phase 2: Analyzing Windows OS Artifacts

Each major artifact category was thoroughly reviewed.

1. Event Log Analysis

Tools Used:

3. Log Parser Studio for querying massive event logs efficiently.
4. Windows Event Viewer for specific manual review.

Key Findings:

5. Windows Security Logs:
   • Event ID 4625 (failed logon): Spotted systematic brute-forcing attempts targeting Admin and Service accounts during non-business hours.
   • Event ID 4648 (explicit credential usage): The attacker leveraged stolen credentials to execute privileged commands remotely.

6. PowerShell Logs:
   • Event ID 4104: Found evidence of obfuscated PowerShell commands executing Base64-encoded payloads retrieved from suspicious IP addresses.
     
     
     Suspicious commands included:

powershell -nop -w hidden -enc [Base64Payload]

The commands indicated attempts to exfiltrate sensitive files compressed into ZIP archives.

7. System Logs:

Event ID 101 from Task Scheduler revealed malicious scheduled tasks configured to download additional payloads and persist across reboots.

2. Registry Analysis

Tools Used:

8. RegRipper to automate extraction and analysis of registry hives.
9. Registry Explorer for in-depth manual inspection.

Key Findings:

10. Persistence Techniques:

Under HKLM\Software\Microsoft\Windows\CurrentVersion\Run, identified registry keys pointing to malicious payloads (e.g. C:\Users\[User]\AppData\Local\temp\svchost.exe).

11. Modified Portions of the SAM and SECURITY Hives:
    
    Found traces of tools like mimikatz, which the attacker used to dump local cached credentials.

12. Disabled Security Controls:

Discovered deliberate modification of security-related configurations:

HKLM\SOFTWARE\Policies\Microsoft\Windows Defender

Value: DisableAntiSpyware = 1

3. File System Activity

Tools Used:

13. Sleuth Kit / Autopsy for filesystem metadata analysis.
14. Bulk Extractor for string carvings (e.g. keywords, IPs, and emails)

Key Findings:

15. Suspicious Directories:

Located staged data in C:\Users\[User]\Documents\TempFiles, consisting of sensitive spreadsheets.

16. Extracted Executable Payloads:
    • Found and analyzed infected payloads disguised as legitimate Windows files, such as “svchost.exe”.
    • Hashes of the executables (e.g., MD5, SHA256) cross-referenced on platforms like VirusTotal, confirming known malicious signatures.

17. Scheduled Exfiltration:

Identified compressed ZIP archives that were routinely uploaded to attacker-controlled external servers.

4. Process Execution

Tools Used:

18. Sysmon for detailed process logging.
19. Volatility for memory forensics to detect malicious processes.

Key Findings:

20. Execution Flow:

Sysmon logs revealed attacker activity chains:

1. Execution of powershell.exe and certutil.exe for command and file retrieval.
2. Launch of malicious scheduled tasks invoking payloads.
   

Memory analysis confirmed in-memory injections into explorer.exe and svchost.exe, tying them back to the C2 infrastructure.

Shellbag Analysis

Using Volatility, identified the attacker’s access to specific directories containing confidential client files.

Correlating Artifacts

Cross-referencing event logs, registry keys, and process metadata enabled tracking of key attacker TTPs, largely aligning with the MITRE ATT&CK Framework.

Phase 3: Containment, Attribution, and Cleanup

Containment Actions

• Blocked external IP addresses detected during PowerShell data exfiltration.
• Disallowed command execution via PowerShell Constrained Language Mode for non-administrative users.

Attribution:

Traced attacker-controlled server domains using OSINT:

• Whois Lookup to identify domain registrants.
• Dnsdumpster and Google Dorks to find additional malicious domains.

Aggregated data revealed connections to known attacker groups associated with previous campaigns.

Mitigation and Remediation

1. Endpoint Hardening:
   • Cleaned registry modifications, removed malicious payloads, and cleared files with PowerShell scripts.
   • Enabled additional logging for PowerShell and scheduled task activities.

2. Credential Protection:
   • Forced organization-wide password resets and enabled MFA (Multi-Factor Authentication) for admin accounts.

3. Network Security Enhancements:
   • Implemented endpoint firewall rules to block suspicious outbound connections (e.g: DNS tunneling).

Lessons Learned

1. Artifact Correlation:

A thorough understanding of Windows artifacts, including event logs, registry changes, file systems, and memory, was essential for figuring out the attacker’s actions.

2. Log Backup Importance:

Missing log data complicated the timeline reconstruction, underscoring how proper logging practices can significantly impact investigations.

Outcome

The attacker was successfully removed from the network, and data exfiltration attempts were halted. The client strengthened its Windows security posture and saw significant cost savings by relying on specific recommended tools.

This case shows the effectiveness of analyzing Windows operating systems, even when resources are limited, and highlights creative approaches needed to address modern day threats.