Detects suspicious indicators for Sha1 Hulud worm

Hunt Hypothesis

This hunt hypothesis targets adversaries leveraging the Sha1 Hulud worm to establish persistent footholds through file system manipulation and lateral movement within Azure Sentinel-monitored endpoints. Proactively hunting for these specific indicators is critical to identify early-stage infections before they propagate across the network, ensuring rapid containment of this high-severity threat vector.

YARA Rule

rule SUSP_JS_NPM_Sha1_Hulud_Nov25 {
   meta:
      description = "Detects suspicious indicators for Sha1 Hulud worm"
      author = "Marius Benthin"
      date = "2025-11-24"
      modified = "2025-12-15"
      reference = "https://www.aikido.dev/blog/shai-hulud-strikes-again-hitting-zapier-ensdomains"
      hash = "62ee164b9b306250c1172583f138c9614139264f889fa99614903c12755468d0"
      score = 70
      id = "511fa6ca-25fe-57d4-a910-277c92d65e4a"
   strings:
      $x1 = "Sha1-Hulud:\\x"
      $x2 = "SHA1HULUD\"`"
   condition:
      filesize < 20MB
      and 1 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 2 string patterns in its detection logic.

References

False Positive Guidance

Here are 5 specific false positive scenarios for the “Sha1 Hulud worm” detection rule, including targeted filters and exclusions:

Antivirus Engine Signature Updates
- Scenario: The enterprise’s endpoint protection suite (e.g., Microsoft Defender or CrowdStrike) performs a scheduled daily update of its virus definition database. This process often generates high-volume SHA1 hash calculations for new signature files that mimic the worm’s file creation patterns.
- Filter/Exclusion: Exclude processes matching MsMpEng.exe (Microsoft Defender) or csagent.exe (CrowdStrike) when they are accessing directories under %ProgramData%\Microsoft\Windows Defender\Platform.
System State Backup Jobs
- Scenario: A nightly scheduled task using Veeam Agent or Windows Server Backup creates a full system image. During the imaging process, the backup engine reads and hashes thousands of system files in rapid succession, triggering the “suspicious indicator” logic due to the sheer volume of file activity.
- Filter/Exclusion: Create an exclusion for the VeeamService.exe or wbengine.exe processes when they are running under the context of a scheduled task named “System State Backup” between 01:00 and 04:00 UTC.
Software Deployment via Configuration Management
- Scenario: An IT administrator deploys a new application patch across the domain using Microsoft Endpoint Configuration Manager (SCCM) or Ansible Tower. The deployment agent pushes binaries to client machines, generating distinct SHA1 hashes for the installed packages that resemble the worm’s propagation behavior.
- Filter/Exclusion: Filter out alerts originating from ccmsetup.exe (SCCM) or ansible-runner where the source IP belongs to the internal management subnet (e.g., 10.20.x.x