WATCOM CCpp 32 Run Time System 1989 1994

Hunt Hypothesis

This hypothesis targets the presence of legacy WATCOM C++ 32-bit run-time libraries, which may indicate the use of outdated or custom-compiled binaries that could harbor hidden backdoors or facilitate low-level memory manipulation by an adversary. Proactively hunting for these artifacts in Azure Sentinel helps identify potentially unmanaged or obfuscated executables that bypass standard application whitelisting, reducing the risk of undetected persistence or privilege escalation mechanisms.

YARA Rule

rule WATCOM_CCpp_32_Run_Time_System_1989_1994: PEiD
{
    strings:
        $a = { 0E 1F 8C C6 B4 ?? 50 BB ?? ?? CD 21 73 ?? 58 CD 21 72 }
    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 Reporting Tool Execution: A business user runs a custom, unmanaged inventory or reporting script (e.g., stock_report.exe) developed in the early 1990s that has not been recompiled. This executable contains the WATCOM C++ 32-bit runtime strings.
  • Filter/Exclusion: Exclude files located in specific application directories (e.g., C:\Apps\LegacyInventory\bin\) or exclude processes where the parent process is a known office suite (e.g., EXCEL.EXE or WINWORD.EXE) launching the legacy tool.
• Backup and Restore Operations: During a scheduled backup job (e.g., Veeam or Commvault), the backup agent scans or restores a legacy application server’s file system, causing the YARA rule to match the binary files on disk or in the backup cache.
  • Filter/Exclusion: Exclude files with extensions .bak, .vbk, or .zip located in backup repositories (e.g., D:\BackupRepo\) or exclude processes initiated by known backup service executables (e.g., veeam.exe, commvaultagent.exe).
• Antivirus Quarantine or Scan Cache: The endpoint protection platform (e.g., CrowdStrike, SentinelOne, or Microsoft Defender) has previously quarantined or cached a legacy binary for analysis, and the YARA rule matches the file in the quarantine folder or temporary scan directory.
  • Filter/Exclusion: Exclude files located in standard AV quarantine paths (e.g., C:\ProgramData\Microsoft\Windows Defender\Quarantine\ or C:\ProgramData\CrowdStrike\quarantine\) or files with the attribute “Hidden” in temporary directories (C:\Temp\, C:\Users\<user>\AppData\Local\Temp\).