EXECryptor2223compressedcodewwwstrongbitcom

Hunt Hypothesis

This detection identifies potential archive-based malware execution patterns associated with the StrongBit domain, which may indicate an adversary utilizing compressed payloads to evade initial signature-based defenses. Proactive hunting for this behavior in Azure Sentinel is essential to uncover early-stage lateral movement or data exfiltration attempts that low-severity alerts might otherwise overlook during routine monitoring.

YARA Rule

rule EXECryptor2223compressedcodewwwstrongbitcom
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E8 00 00 00 00 58 [5] 8B 1C 24 81 EB [4] B8 [4] 50 6A 04 68 00 10 00 00 50 6A 00 B8 C4 [3] 8B 04 18 FF D0 59 BA [4] 01 DA 52 53 50 89 C7 89 D6 FC F3 A4 B9 [4] 01 D9 FF D1 58 8B 1C 24 68 00 80 00 00 6A 00 50 }
	$a1 = { E8 00 00 00 00 58 [5] 8B 1C 24 81 EB [4] B8 [4] 50 6A 04 68 00 10 00 00 50 6A 00 B8 C4 [3] 8B 04 18 FF D0 59 BA [4] 01 DA 52 53 50 89 C7 89 D6 FC F3 A4 B9 [4] 01 D9 FF D1 58 8B 1C 24 68 00 80 00 00 6A 00 50 B8 C8 [3] 8B 04 18 FF D0 59 58 5B 83 EB 05 C6 03 B8 43 89 03 83 C3 04 C6 03 C3 09 C9 74 46 89 C3 E8 A0 00 00 00 FC AD 83 F8 FF 74 38 53 89 CB 01 C3 01 0B 83 C3 04 AC 3C FE 73 07 25 FF 00 00 00 EB ED 81 C3 FE 00 00 00 09 C0 7A 09 66 AD 25 FF FF 00 00 EB DA AD 4E 25 FF FF FF 00 3D FF FF FF 00 75 CC [5] C3 }

condition:
		$a0 or $a1
}

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 2 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the EXECryptor2223compressedcodewwwstrongbitcom detection rule, including suggested filters and exclusions:

• Scenario: Automated Backup Compression by Veeam

  • Context: The enterprise uses Veeam Backup & Replication to perform nightly incremental backups. During the process, the vbr.exe service compresses large database snapshots into .zip or proprietary archive formats before transmission. This compression activity triggers the YARA rule due to the “compressed code” signature matching the StrongBit pattern.
  • Filter/Exclusion: Add a whitelist entry for the Veeam executable path: C:\Program Files\Veeam\Backup and Replication\Backup\VBService.exe (and its child processes) with an exclusion on the specific YARA rule ID.

• Scenario: Microsoft Office 365 Click-to-Run Updates

  • Context: The Office Click-to-Run service (OfficeC2RClient.exe) periodically downloads and installs feature updates or language packs. These updates are often delivered as compressed .cab or .msi packages that contain embedded encrypted code segments similar to the StrongBit signature, causing a trigger during the installation phase.
  • Filter/Exclusion: Create an exclusion based on the parent process OfficeClickToRun.exe and filter out events where the file extension is .cab or .msi originating from the Microsoft Update service account (NT SERVICE\O365C2R).

• Scenario: Antivirus Heuristic Scanning by CrowdStrike

  • Context: The endpoint protection suite (CrowdStrike Falcon) performs real-time heuristic scanning on newly created files. When a user saves a large document or archive, the Falcon sensor (FalconService.exe) scans and temporarily compresses the file in memory