Auto-generated rule - file dc18850d065ff6a8364421a9c8f9dd5fcce6c7567f4881466cee00e5cd0c7aa8

Hunt Hypothesis

This detection rule identifies potential adversary behavior involving unauthorized file access and exfiltration through Azure storage, leveraging suspicious file activity patterns. SOC teams should proactively hunt for this behavior to detect and mitigate advanced persistent threats that exploit cloud storage for data theft or command and control operations.

YARA Rule

rule CheshireCat_Sample2
{

    meta:
        description = "Auto-generated rule - file dc18850d065ff6a8364421a9c8f9dd5fcce6c7567f4881466cee00e5cd0c7aa8"
        author = "Florian Roth"
        reference = "https://malware-research.org/prepare-father-of-stuxnet-news-are-coming/"
        date = "2015-08-08"
        score = 70
        hash = "dc18850d065ff6a8364421a9c8f9dd5fcce6c7567f4881466cee00e5cd0c7aa8"

    strings:
        $s0 = "mpgvwr32.dll" fullword ascii
        $s1 = "Unexpected failure of wait! (%d)" fullword ascii
        $s2 = "\"%s\" /e%d /p%s" fullword ascii
        $s4 = "error in params!" fullword ascii
        $s5 = "sscanf" fullword ascii
        $s6 = "<>Param : 0x%x" fullword ascii

    condition:
        uint16(0) == 0x5a4d and filesize < 100KB and 4 of ($s*)
}

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 6 string patterns in its detection logic.

References

False Positive Guidance

Scenario: A system administrator is using PowerShell to perform routine system cleanup tasks, such as removing temporary files or logs.
Filter/Exclusion: process.name != "powershell.exe" OR process.args contains "Cleanup" OR "Clear-Item"
Scenario: A scheduled job runs nightly to archive old data using a script that temporarily creates and deletes files.
Filter/Exclusion: process.name contains "schtasks.exe" OR process.parent.name contains "TaskScheduler"
Scenario: A backup tool like Veeam or Commvault is performing a backup operation that involves creating and deleting temporary files.
Filter/Exclusion: process.name contains "veeam" OR "commvault" OR process.parent.name contains "backup"
Scenario: An IT admin is using Windows Event Viewer or PowerShell to investigate system logs and manually deletes log files.
Filter/Exclusion: process.name contains "eventvwr.exe" OR "powershell.exe" AND process.args contains "Delete-Item" OR "Remove-Item"
Scenario: A CI/CD pipeline (e.g., Jenkins, GitLab CI) runs a script that creates and deletes temporary files during a deployment.
Filter/Exclusion: process.name contains "jenkins.exe" OR "gitlab-runner" OR process.parent.name contains "ci" OR "cd"