Insider Threat DLP Obfuscation Analysis Identity Logs

Insider threats are notoriously difficult to detect because actors leverage legitimate credentials and authorized administrative access. This case study details the forensic investigation of Project CryptoStealer, an internal threat actor who abused privileged domain access to locate and exfiltrate database credential backups and certificate private keys from a staging server.

Vector

Legitimate administrative session misuse paired with custom obfuscated PowerShell scripts.

Telemetry

Windows Event Logs (Security channel: Event IDs 4624, 4672) correlated with EDR process command lines.

Exfiltration

Sensitive configuration backups moved outbound via DNS tunneling payloads.

Contents

  1. Anomaly Detection & Initial Alerts
  2. Identity Correlation & Session Hijacking
  3. De-obfuscating the PowerShell Payload
  4. Accessing the Credential Vault
  5. Detection & Hunting KQL Queries
  6. Prevention & Access Control Controls

1. Anomaly Detection & Initial Alerts

The incident was identified when the SOC received a threat alert detailing a high volume of DNS query requests targeting a subdomain of aws-update-service.net from a system hosting a critical staging application database (STG-DB-02).

A standard DNS lookup of the domain showed it was not owned by Amazon Web Services, but rather registered through a private domain service in Eastern Europe. The query logs showed a repetitive sequence of TXT and A-record queries carrying hex-encoded subdomains, characteristic of DNS exfiltration (tunneling).

2. Identity Correlation & Session Hijacking

Security analysts reviewed authentication logs for STG-DB-02. They found a successful Logon Session (Event ID 4624) corresponding to a senior engineer's administrator account:

  • Logon Type: Type 3 (Network Logon) via SMB / Kerberos.
  • Source Network Address: 10.10.14.88 (assigned to a contractor workstation).
  • Privileges: Event ID 4672 (Special privileges assigned: SeDebugPrivilege, SeBackupPrivilege).

The engineer associated with the logon was confirmed to be out of the office on annual leave, pointing to either session theft, remote credential theft, or malicious insider activity using shared credentials.

3. De-obfuscating the PowerShell Payload

Process audit log events (Event ID 4688) showed that the compromised user session spawned a PowerShell process with a highly obfuscated command line: 

powershell.exe -w hidden -c "$s='txet.tseuqerderc\pmt\swodniw\:c egapkaB-tcatxE.tpyrcsnwod$'; iex ($s.ToCharArray() | % {$o += $_}; [Array]::Reverse($o); $o -join '')"

Let's deconstruct the script to understand how it bypasses signature-based security rules:

  1. The variable $s holds a reversed string: 'txet.tseuqerderc\pmt\swodniw\:c egapkaB-tcatxE.tpyrcsnwod$'.
  2. $s.ToCharArray() | % {$o += $_}; [Array]::Reverse($o); $o -join '' converts the string to an array, reverses the character order, and joins them back together.
  3. Evaluating the reversed string yields the actual payload: $downscript.Extract-Backupage c:\windows\temp\credrequest.text.

The decrypted target file (credrequest.text) contained script instructions to copy registry hive keys using native utilities to obtain local password hashes: 

reg save HKLM\SAM C:\windows\temp\sam.bak
reg save HKLM\SYSTEM C:\windows\temp\system.bak

4. Accessing the Credential Vault

Using the local admin privileges, the attacker targeted staging database connection strings and TLS private key certificates stored in the system vault: 

Get-ChildItem Cert:\LocalMachine\My | Export-Certificate -Type CERT -FilePath C:\windows\temp\server_key.cer

The data was packed into a byte stream and chunked via the rogue AWS update subdomain using an automated DNS utility script, transmitting small pieces of data within DNS query host headers.

5. Detection & Hunting KQL Queries

Implement these KQL rules inside your SIEM to monitor for administrative session misuse and command-line string reversal tricks.

Detecting PowerShell Command String Reversals

DeviceProcessEvents
| where ProcessCommandLine contains "Reverse" or ProcessCommandLine contains "ToCharArray"
| where ProcessCommandLine contains "iex" or ProcessCommandLine contains "Invoke-Expression"
| project TimeGenerated, DeviceName, InitiatingProcessFileName, ProcessCommandLine, AccountName

Anomalous Registry Save Operations

DeviceProcessEvents
| where FileName =~ "reg.exe"
| where ProcessCommandLine contains "save" and (ProcessCommandLine contains "SAM" or ProcessCommandLine contains "SYSTEM" or ProcessCommandLine contains "SECURITY")
| project TimeGenerated, DeviceName, FileName, ProcessCommandLine, AccountName, FolderPath

6. Prevention & Access Control Controls

Hardening Recommendations
  • Disable Registry Export: Restrict non-system execution access to reg.exe and regedit.exe.
  • Enforce Logon Boundaries: Restrict local administrative logins from network segments that contain user workstations.
  • DNS Tunneling Detection: Enable machine-learning threat detection in local firewalls and domain controllers to flag anomalous high-frequency subdomain requests.