LinuxMrBlack

Hunt Hypothesis

The LinuxMrBlack rule detects potential adversary behavior involving suspicious file artifacts commonly associated with malware or persistence mechanisms on Linux systems. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate early-stage threats that may evade traditional detection methods.

YARA Rule

rule LinuxMrBlack
{
    meta:
	Author      = "@benkow_"
        Date        = "2014/09/12" 
        Description = "Strings inside"
        Reference   = "http://www.kernelmode.info/forum/viewtopic.php?f=16&t=3483"

    strings:
        $a = "Mr.Black"
	$b = "VERS0NEX:%s|%d|%d|%s"
    condition:
        $a and $b
}

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.

• Source Rule

False Positive Guidance

• Scenario: Legitimate system update via package manager
  Description: A system administrator runs a package update using apt or yum, which may trigger the rule due to similar file names or content.
  Filter/Exclusion: Check for presence of /usr/bin/apt or /usr/bin/yum in the process command line, or filter by process name.

• Scenario: Scheduled backup job using rsync
  Description: A scheduled backup job using rsync copies large amounts of data, which may resemble malicious file transfer behavior.
  Filter/Exclusion: Filter by process name rsync or check for presence of /usr/bin/rsync in the command line.

• Scenario: Admin task using tar to archive logs
  Description: An administrator uses tar to archive log files, which may trigger the rule due to similar command patterns.
  Filter/Exclusion: Filter by process name tar or check for presence of /usr/bin/tar in the command line.

• Scenario: Legitimate cron job for log rotation
  Description: A cron job runs log rotation using logrotate, which may trigger the rule due to file operations.
  Filter/Exclusion: Filter by process name logrotate or check for presence of /usr/sbin/logrotate in the command line.

• Scenario: User-generated script using Python for data processing
  Description: A user runs a Python script for data processing that creates temporary files, which may be flagged by the rule.
  Filter/Exclusion: Filter by process name python or check for presence of /usr/bin/python in the command line, and verify the script path is in a user-owned directory.