Detects a POC to turn Microsoft Warbird into a shellcode loader

Hunt Hypothesis

This hunt hypothesis targets adversaries who exploit the Microsoft Warbird component as a shellcode loader to establish persistence and execute arbitrary code within the environment. Proactively hunting for this behavior in Azure Sentinel is critical because it identifies early-stage post-exploitation activities that could lead to lateral movement or data exfiltration if left undetected.

YARA Rule

rule MAL_POC_Microsoft_Warbird_Loader_Feb26 {
   meta:
      description = "Detects a POC to turn Microsoft Warbird into a shellcode loader"
      author = "X__Junior"
      date = "2026-02-03"
      reference = "https://cirosec.de/en/news/abusing-microsoft-warbird-for-shellcode-execution/"
      hash = "29d0467ee452752286318f350ceb28a2b04ee4c6de550ba0edc34ae0fa7cbb03"
      score = 75
      id = "a07f6d10-c463-56a6-a667-82b1c00760af"
   strings:
      $op = { fe af fe ca ef be ad de }
   condition:
      uint16(0) == 0x5a4d and $op
}

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 1 string patterns in its detection logic.

References

False Positive Guidance

Here are 5 specific false positive scenarios for the “Detects a POC to turn Microsoft Warbird into a shellcode loader” rule, including targeted filters and exclusions:

Scenario: Automated Patch Deployment via SCCM
- Context: System Center Configuration Manager (SCCM) or Microsoft Endpoint Configuration Manager pushes large software updates. During the installation phase, the msiexec.exe process often spawns a temporary helper process that loads shellcode to execute post-installation scripts or registry modifications, mimicking the Warbird behavior.
- Filter/Exclusion: Exclude processes where the parent process is ccmsetup.exe (SCCM Setup) and the executable path contains \Microsoft\CCM\. Additionally, filter out events where the command line includes specific SCCM arguments like /install or /action:repair.
Scenario: Scheduled Antivirus Deep Scan
- Context: Enterprise antivirus solutions such as Microsoft Defender for Endpoint or CrowdStrike Falcon perform scheduled deep scans. These agents often utilize a custom loader mechanism (similar to Warbird) to inject scanning modules into memory without triggering the main UI, which can look like shellcode loading.
- Filter/Exclusion: Create an exclusion based on the process image name being MsMpEng.exe (Defender), CsFalconService.exe (CrowdStrike), or rtvscan64.exe (Symantec). Ensure the filter applies when the process is running under a scheduled task context (e.g., parent PID belonging to svchost.exe with specific service names like WSearch or Antimalware Service).
Scenario: Office 365 Click-to-Run Updates
- Context: The Microsoft Office Click-to-Run update mechanism (OfficeClickToRun.exe) frequently launches background workers to apply hotfixes. These