Obsidium v10061 additional

Hunt Hypothesis

This rule detects the presence of the Obsidium v10061 malware variant, which is often deployed to establish a foothold or execute malicious payloads within the environment. Proactively hunting for this specific signature allows the SOC team to identify compromised hosts early, potentially preventing lateral movement or data exfiltration before the adversary achieves their operational objectives.

YARA Rule

rule Obsidium_v10061_additional: PEiD
{
    strings:
        $a = { E8 AF 1C 00 00 }
    condition:
        $a at pe.entry_point

}

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 1 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Legacy .NET Application Updates: A common false positive occurs when enterprise applications built on older versions of the .NET Framework (e.g., .NET 3.5 or 4.0) are updated via Windows Update or vendor-specific patching tools like WSUS or SCCM. These updates often involve temporary DLLs or assemblies that may match generic YARA signatures for Obsidium if the rule relies on broad string matches or entropy checks common in older malware families.

  • Filter/Exclusion: Exclude processes originating from known update service paths such as C:\Windows\SoftwareDistribution\ or C:\Windows\Installer\, and specifically allow executables named wuaexerver.exe or wuauclt.exe during the update window.

• Antivirus/EDR Self-Scanning and Quarantine: Security suites like CrowdStrike Falcon, SentinelOne, or Microsoft Defender for Endpoint frequently create temporary copies of quarantined files or perform deep scans of memory dumps. If the YARA rule includes patterns that match generic PE headers or specific byte sequences found in legitimate but complex binaries, these self-scan operations can trigger alerts.

  • Filter/Exclusion: Exclude processes running from the vendor’s specific installation directories (e.g., C:\Program Files\CrowdStrike\ or C:\Program Files\Microsoft Security Client\) and filter out events where the parent process is the security agent itself (e.g., FalconSensor.exe or MsMpEng.exe).

• Database Maintenance and Backup Jobs: Scheduled jobs for database maintenance tools such as SQL Server Agent or Oracle RMAN can generate temporary binary files or log segments that might be misidentified by YARA rules if they contain specific binary structures or checksums. This is particularly common in environments where backups are compressed or encrypted using proprietary algorithms that resemble