DEF10bartxt

Hunt Hypothesis

This YARA rule targets specific file patterns associated with the “DEF10bartxt” signature, potentially indicating the presence of a low-severity artifact or known benign file that may be leveraged for staging or initial reconnaissance. Proactively hunting for this pattern in Azure Sentinel allows the SOC team to identify anomalous file placements or unexpected artifacts that could serve as footholds for more complex attack chains or indicate misconfigurations in the environment.

YARA Rule

rule DEF10bartxt
{
      meta:
		author="malware-lu"
strings:
		$a0 = { BE [2] 40 00 6A ?? 59 80 7E 07 00 74 11 8B 46 0C 05 00 00 40 00 8B 56 10 30 10 40 4A 75 FA 83 C6 28 E2 E4 68 [2] 40 00 C3 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 }

condition:
		$a0 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 Application Deployment via Group Policy: When IT administrators deploy legacy Windows applications (e.g., older versions of Adobe Acrobat, Java, or specific banking plugins) that rely on outdated text-based configuration files or embedded scripts, the YARA rule DEF10bartxt may match the binary or script content.
  • Filter/Exclusion: Exclude processes originating from known deployment paths (e.g., C:\Windows\Installer\, C:\Program Files\LegacyApps\) or filter by specific parent processes like gpupdate.exe or msiexec.exe when the file hash matches known good versions of these legacy tools.
• Scheduled Backup and Archiving Jobs: Enterprise backup solutions (e.g., Veeam, Commvault, or Windows Server Backup) often create temporary text-based manifests, logs, or metadata files during the backup cycle. If these files contain specific string patterns defined in the DEF10bartxt rule, they can trigger false positives.
  • Filter/Exclusion: Exclude files located in standard backup directories (e.g., C:\Backup\, D:\Archive\, or specific Veeam repository paths) and filter events where the parent process is a known backup agent (e.g., vssadmin.exe, wbadmin.exe, or vendor-specific executables).
• Development and Build Artifacts: In software development environments, build tools (e.g., MSBuild, Gradle, or npm) generate temporary text files, configuration dumps, or debug logs that may contain string literals matching the rule’s criteria. This is common in CI/CD pipelines running on build agents.
  • Filter/Exclusion: Exclude processes associated with build tools (e.g., msbuild.exe, gradle.bat, node.exe) and filter files located in common build output directories (e.g., bin\, `obj