APT Derusbi Gen | SOC Hunt Feed

Hunt Hypothesis

The hypothesis is that the detection identifies potential generation of Derusbi malware by an adversary leveraging custom code generation techniques to evade traditional signature-based detection. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify early-stage APT activity and prevent lateral movement and data exfiltration.

YARA Rule

rule APT_Derusbi_Gen
{

meta:
    author = "ThreatConnect Intelligence Research Team"

strings:
    $2 = "273ce6-b29f-90d618c0" wide ascii
    $A = "Ace123dx" fullword wide ascii
    $A1 = "Ace123dxl!" fullword wide ascii
    $A2 = "Ace123dx!@#x" fullword wide ascii
    $C = "/Catelog/login1.asp" wide ascii
    $DF = "~DFTMP$$$$$.1" wide ascii
    $G = "GET /Query.asp?loginid=" wide ascii
    $L = "LoadConfigFromReg failded" wide ascii
    $L1 = "LoadConfigFromBuildin success" wide ascii
    $ph = "/photoe/photo.asp HTTP" wide ascii
    $PO = "POST /photos/photo.asp" wide ascii
    $PC = "PCC_IDENT" wide ascii

condition:
    any of them
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

Microsoft Defender for Endpoint — Custom indicators / advanced hunting
Email Gateway — Attachment scanning
File Share Monitoring — Periodic scanning of shared drives
YARA CLI — Manual threat hunting on endpoints

This rule contains 12 string patterns in its detection logic.

Source Rule

False Positive Guidance

Scenario: Legitimate scheduled system maintenance job using schtasks.exe
Filter/Exclusion: process.parent_process == "schtasks.exe" or process.name == "schtasks.exe"
Scenario: Admin using reg.exe to modify registry settings during routine configuration
Filter/Exclusion: process.name == "reg.exe" and process.parent_process != "explorer.exe"
Scenario: IT staff using PowerShell to automate user account management via Invoke-Command
Filter/Exclusion: process.name == "powershell.exe" and process.command_line contains "Invoke-Command"
Scenario: System update process using msiexec.exe to install patches
Filter/Exclusion: process.name == "msiexec.exe" and process.command_line contains "/i"
Scenario: Database backup using sqlcmd.exe with scheduled task
Filter/Exclusion: process.name == "sqlcmd.exe" and process.parent_process == "schtasks.exe"