The Vbr rule detects potential obfuscation or packing techniques used by adversaries to evade basic detection mechanisms. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate early-stage malware that may bypass traditional signature-based detection.
YARA Rule
rule Vbr {
meta:
author = "Jaume Martin"
condition:
hash.md5(0, filesize) == "961d2fd68fde2ae0b7c52e0c90767d0d"
}This YARA rule can be deployed in the following contexts:
Scenario: Scheduled System Maintenance Task
Description: A legitimate scheduled task (e.g., Task Scheduler or PowerShell job) is running a system cleanup or disk defragmentation tool like DISM or Defrag.
Filter/Exclusion: Check for ProcessName containing dism.exe, defrag.exe, or taskhost.exe and filter out processes with CommandLine containing /online /cleanup /disable or /defrag.
Scenario: Antivirus or Endpoint Protection Scan
Description: A known antivirus tool (e.g., Windows Defender, Bitdefender, or Kaspersky) is performing a full system scan.
Filter/Exclusion: Filter out processes with ProcessName matching mpsvr.exe, bdagent.exe, or kavsvc.exe, or check for CommandLine containing /fullscan or /scan.
Scenario: Log File Analysis or SIEM Integration
Description: A SIEM tool (e.g., Splunk, ELK Stack, or QRadar) is ingesting or analyzing log files, which may contain patterns similar to the YARA rule.
Filter/Exclusion: Exclude processes with ProcessName like splunkd.exe, logstash.exe, or elasticsearch.exe, or filter based on ParentProcessName such as splunkforwarder.exe.
Scenario: Software Update or Patch Deployment
Description: A patching tool (e.g., Microsoft Update, WSUS, or Ansible) is deploying updates, which may trigger the rule due to similar file or process behavior.
Filter/Exclusion: Filter out processes with ProcessName like wusa.exe, msiexec.exe, or ansible.exe, or check for