This rule detects a new variant of Marcher

Hunt Hypothesis

A new variant of the Marcher malware is being executed in the environment, indicating potential data exfiltration or lateral movement. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate early-stage compromises before significant data loss occurs.

YARA Rule

rule marcher_v2
{
	meta:
		description = "This rule detects a new variant of Marcher"
		sample = "27c3b0aaa2be02b4ee2bfb5b26b2b90dbefa020b9accc360232e0288ac34767f"
		author = "Antonio S. <[email protected]>"
		source = "https://analyst.koodous.com/rulesets/1301"
	strings:
		$a = /assets\/[a-z]{1,12}.datPK/
		$b = "mastercard_img"
		$c = "visa_verifed"

	condition:
		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 3 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: Legitimate scheduled backup job using rsync
  Description: A scheduled backup job using rsync may trigger the rule due to the use of similar command-line arguments or file paths as seen in malicious activity.
  Filter/Exclusion: Check for the presence of /usr/bin/rsync in the process path and filter out processes associated with known backup tools like rsync, borgbackup, or duplicity.

• Scenario: System update via apt or yum
  Description: A system update process using apt or yum may generate similar network activity or file modifications as the Marcher malware, especially if the update involves downloading packages from a legitimate repository.
  Filter/Exclusion: Filter processes that match known package managers (apt, yum, dnf) and exclude traffic to official repositories (e.g., archive.ubuntu.com, repo.centos.org).

• Scenario: Admin task using wget or curl for configuration sync
  Description: An administrator may use wget or curl to fetch configuration files from an internal server, which could resemble the behavior of a malware downloader.
  Filter/Exclusion: Filter processes that match known admin tools (wget, curl) and exclude traffic to internal IP ranges or known internal configuration servers.

• Scenario: Logrotate job executing scripts
  Description: The logrotate utility may execute scripts during log rotation, which could trigger the rule if the script path or command-line arguments resemble those of a malicious payload.
  Filter/Exclusion: Filter processes with /usr/sbin/logrotate in the path and exclude any script execution that occurs during known log rotation windows (e.g., during off-peak hours or on specific log files).

• Scenario: Antivirus or endpoint protection tool scanning