The hex_script rule detects potential obfuscation techniques where adversaries may encode or hide malicious payloads within hexadecimal data to evade basic detection mechanisms. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate early-stage adversarial activity that could lead to more sophisticated attacks.
YARA Rule
rule hex_script {
strings:
$ = "\\x73\\x63\\x72\\x69\\x70\\x74\\x22"
condition:
any of them and filesize < 500KB
}
This YARA rule can be deployed in the following contexts:
Scenario: Scheduled System Update via Windows Update
Description: A legitimate scheduled task runs Windows Update, which may include hex-encoded data in temporary files.
Filter/Exclusion: process.name != "wuauclt.exe" or process.parent.name != "taskeng.exe"
Scenario: Hex Dump Generation for Debugging
Description: A developer uses xxd (Linux) or certutil -encode (Windows) to generate hex dumps for debugging purposes.
Filter/Exclusion: process.name contains "xxd" or process.name contains "certutil" and process.args contains "-encode"
Scenario: Admin Task Using Hex Data for File Conversion
Description: An admin uses base64 or hexdump tools to convert files for archival or transfer.
Filter/Exclusion: process.name contains "hexdump" or process.name contains "base64" and process.args contains "convert"
Scenario: Malware Analysis Environment
Description: A sandbox or analysis environment uses hex data for testing or analysis of malicious files.
Filter/Exclusion: process.parent.name contains "vmtoolsd" or process.parent.name contains "qemu" or process.name contains "sandbox"
Scenario: Hexadecimal Data in Log Files
Description: Log files or system messages contain hex data as part of normal operations (e.g., network packet dumps).
Filter/Exclusion: file.path contains "log" or file.path contains "syslog" or file.path contains "eventlog"