md5 825a3b2a6abbe6abcdeda64a73416b3d

Hunt Hypothesis

The rule detects the presence of a specific MD5 hash associated with potentially malicious code, indicating possible adversary activity involving file execution or persistence. 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 md5_825a3b2a6abbe6abcdeda64a73416b3d {
	/*
    // $ooooo00oo0000oo0oo0oo00ooo0ooo0o0o0 = gethostbyname($_SERVER["SERVER_NAME"]);
    // if(!oo00o0OOo0o00O("fsockopen"))
    // strings: $ = "$ooooo00oo0000oo0"
    */
    strings: $ = /[o0O]{3}\("fsockopen"\)/
    condition: any 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
• Source Rule

False Positive Guidance

• Scenario: Legitimate system update using Microsoft Update
  Filter/Exclusion: Exclude files signed by Microsoft with SHA256 hash matching known update packages
  Example: file.hash.sha256 == "a1b2c3d4e5f67890..." or file.signer == "Microsoft Corporation"

• Scenario: Scheduled backup job using Veeam Backup & Replication
  Filter/Exclusion: Exclude files with process name veeam.exe or vbackup.exe
  Example: process.name == "veeam.exe"

• Scenario: Admin task using PowerShell for log cleanup
  Filter/Exclusion: Exclude PowerShell scripts executed by PowerShell.exe with log or clean in the command line
  Example: process.name == "PowerShell.exe" && command_line contains "log" or "clean"

• Scenario: Antivirus signature update using Bitdefender
  Filter/Exclusion: Exclude files with process name bdagent.exe or bdupdater.exe
  Example: process.name == "bdagent.exe"

• Scenario: Database backup using MySQL scheduled task
  Filter/Exclusion: Exclude files with process name mysqldump.exe or mysql.exe
  Example: process.name == "mysqldump.exe"