This detection rule identifies potential adversary behavior involving unauthorized file access or exfiltration through Azure storage, leveraging unusual file activity patterns that may indicate data theft or persistence. SOC teams should proactively hunt for this behavior in Azure Sentinel to detect and mitigate advanced threats that exploit cloud storage infrastructure.
YARA Rule
rule CheshireCat_Gen1
{
meta:
description = "Auto-generated rule - file ec41b029c3ff4147b6a5252cb8b659f851f4538d4af0a574f7e16bc1cd14a300"
author = "Florian Roth"
reference = "https://malware-research.org/prepare-father-of-stuxnet-news-are-coming/"
date = "2015-08-08"
super_rule = 1
score = 90
hash1 = "ec41b029c3ff4147b6a5252cb8b659f851f4538d4af0a574f7e16bc1cd14a300"
hash2 = "32159d2a16397823bc882ddd3cd77ecdbabe0fde934e62f297b8ff4d7b89832a"
hash3 = "63735d555f219765d486b3d253e39bd316bbcb1c0ec595ea45ddf6e419bef3cb"
hash4 = "c074aeef97ce81e8c68b7376b124546cabf40e2cd3aff1719d9daa6c3f780532"
strings:
$x1 = "CAPESPN.DLL" fullword wide
$x2 = "WINF.DLL" fullword wide
$x3 = "NCFG.DLL" fullword wide
$x4 = "msgrthlp.dll" fullword wide
$x5 = "Local\\{c0d9770c-9841-430d-b6e3-575dac8a8ebf}" fullword ascii
$x6 = "Local\\{1ef9f94a-5664-48a6-b6e8-c3748db459b4}" fullword ascii
$a1 = "Interface\\%s\\info" fullword ascii
$a2 = "Interface\\%s\\info\\%s" fullword ascii
$a3 = "CLSID\\%s\\info\\%s" fullword ascii
$a4 = "CLSID\\%s\\info" fullword ascii
$b1 = "Windows Shell Icon Handler" fullword wide
$b2 = "Microsoft Shell Icon Handler" fullword wide
$s1 = "\\StringFileInfo\\%s\\FileVersion" fullword ascii
$s2 = "CLSID\\%s\\AuxCLSID" fullword ascii
$s3 = "lnkfile\\shellex\\IconHandler" fullword ascii
$s4 = "%s: %s, %.2hu %s %hu %2.2hu:%2.2hu:%2.2hu GMT" fullword ascii
$s5 = "%sMutex" fullword ascii
$s6 = "\\ShellIconCache" fullword ascii
$s7 = "+6Service Pack " fullword ascii
condition:
uint16(0) == 0x5a4d and filesize < 350KB and 7 of ($s*) and 2 of ($a*) and 1 of ($b*) and 1 of ($x*)
}This YARA rule can be deployed in the following contexts:
This rule contains 19 string patterns in its detection logic.
Scenario: Scheduled System Maintenance Task
Description: A legitimate scheduled task (e.g., Task Scheduler or cron job) is running a script that temporarily creates or modifies files matching the rule’s criteria.
Filter/Exclusion: Exclude events where the process is associated with a known system maintenance task (e.g., schtasks.exe, at.exe, or crontab).
Scenario: Software Update or Patch Installation
Description: A patch or update (e.g., via Windows Update, Chocolatey, or Ansible) is being installed, which creates temporary files or modifies existing ones.
Filter/Exclusion: Exclude events where the process is associated with an update tool (e.g., wusa.exe, choco, or ansible-playbook).
Scenario: Log File Rotation or Archiving
Description: A log rotation tool (e.g., logrotate, rsyslog, or Windows Event Log Management) is archiving or rotating logs, which may trigger file creation or modification.
Filter/Exclusion: Exclude events where the process is related to log management (e.g., logrotate, rsyslog, or eventvwr.exe).
Scenario: Backup or Sync Job Execution
Description: A backup tool (e.g., Veeam, Acronis, or rsync) is performing a backup or synchronization task, which may involve file operations.
Filter/Exclusion: Exclude events where the process is associated with a backup tool (e.g., veeam.exe, acronis, or rsync).
Scenario: Admin User Performing File Management
Description: An admin user is manually moving, copying, or renaming files using tools like Robocopy, `PowerShell