Detects Malware from Greenbug Incident

Hunt Hypothesis

Adversaries may use custom malware associated with the Greenbug incident to establish persistence and exfiltrate data within Azure environments. SOC teams should proactively hunt for this behavior to identify and mitigate potential long-term compromise and data theft.

YARA Rule

rule Greenbug_Malware_1 {
   meta:
      description = "Detects Malware from Greenbug Incident"
      author = "Florian Roth"
      reference = "https://goo.gl/urp4CD"
      date = "2017-01-25"
      hash1 = "dab460a0b73e79299fbff2fa301420c1d97a36da7426acc0e903c70495db2b76"
   strings:
      $s1 = "vailablez" fullword ascii
      $s2 = "Sfouglr" fullword ascii
   condition:
      ( uint16(0) == 0x5a4d and filesize < 400KB and all 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

Scenario: Scheduled System Maintenance Job
Description: A legitimate scheduled task runs a script that temporarily downloads a file from a known internal repository, which may trigger the rule due to file source or content similarity.
Filter/Exclusion: Exclude files originating from internal repositories (e.g., C:\Tools\InternalRepo\*) or use a filter based on the source IP or domain (src_ip = 10.0.0.100).
Scenario: Admin Performing Software Update
Description: An administrator is manually updating a system using a known trusted tool (e.g., Microsoft Update or a company-approved patching tool), which may contain a file with similar characteristics to the malicious payload.
Filter/Exclusion: Exclude processes initiated by admin users with elevated privileges (user = admin) or filter by process name (process.name = "wuauclt.exe").
Scenario: Log File Analysis by SIEM Tool
Description: A Security Information and Event Management (SIEM) tool (e.g., Splunk, ELK) is parsing log files and generating a file that matches the signature of the Greenbug malware.
Filter/Exclusion: Exclude files with a known log file extension (e.g., .log, .csv) or filter based on the process name (process.name = "splunkd.exe" or process.name = "logstash").
Scenario: Automated Backup Job
Description: A backup job (e.g., using Veeam or Acronis) is transferring files between servers, and the transfer process includes a file that matches the malware signature due to similar file structure.
Filter/Exclusion: Exclude files associated with backup processes (process.name = "veeam.exe" or process.name = "acronisbackup.exe") or filter by file path (`file.path =