RLPackAp0x

Hunt Hypothesis

This detection identifies the presence of RLPackAp0x-packed executables, which adversaries often utilize to obfuscate malicious payloads and evade signature-based analysis within the Azure Sentinel environment. Proactively hunting for this pattern allows the SOC team to uncover stealthy threats that may bypass standard antivirus solutions by analyzing file structures before they execute or spread across the network.

YARA Rule

rule RLPackAp0x
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 E8 00 00 00 00 8B 2C 24 83 C4 04 8D B5 2C 0A 00 00 8D 9D 22 02 00 00 33 FF E8 83 01 00 00 6A 40 68 00 10 00 00 68 00 20 0C 00 6A 00 FF 95 CD 09 00 00 89 85 14 0A 00 00 EB 14 60 FF B5 14 0A }
	$a1 = { 60 E8 00 00 00 00 8B 2C 24 83 C4 04 8D B5 5A 0A 00 00 8D 9D 40 02 00 00 33 FF E8 83 01 00 00 6A 40 68 00 10 00 00 68 00 20 0C 00 6A 00 FF 95 EB 09 00 00 89 85 3A 0A 00 00 EB 14 60 FF B5 3A 0A }
	$a2 = { 60 E8 00 00 00 00 8B 2C 24 83 C4 04 EB 03 0C 00 00 EB 03 0C 00 00 8D B5 CB 22 00 00 8D 9D F0 02 00 00 33 FF E8 47 02 00 00 EB 03 15 00 00 6A 40 68 00 10 00 00 68 00 20 0C 00 6A 00 FF 95 9B 0A }
	$a3 = { 60 E8 00 00 00 00 8B 2C 24 83 C4 04 8D B5 2C 0A 00 00 8D 9D 22 02 00 00 33 FF E8 [4] 6A 40 68 [4] 68 [4] 6A 00 FF 95 CD 09 00 00 89 85 [4] EB 14 60 FF B5 14 0A }
	$a4 = { 60 E8 00 00 00 00 8B 2C 24 83 C4 04 8D B5 5A 0A 00 00 8D 9D 40 02 00 00 33 FF E8 [4] 6A 40 68 [4] 68 [4] 6A 00 FF 95 EB 09 00 00 89 85 [4] EB 14 60 FF B5 3A 0A }
	$a5 = { 60 E8 00 00 00 00 8B 2C 24 83 C4 04 EB 03 [3] EB 03 [3] 8D B5 CB 22 00 00 8D 9D F0 02 00 00 33 FF E8 [4] EB 03 [3] 6A 40 68 [4] 68 [4] 6A 00 FF 95 9B 0A }

condition:
		$a0 at pe.entry_point or $a1 at pe.entry_point or $a2 at pe.entry_point or $a3 at pe.entry_point or $a4 at pe.entry_point or $a5 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 6 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the RLPackAp0x detection rule, along with suggested filters and exclusions tailored for an enterprise environment:

• Scenario: Automated Deployment of Microsoft Office Updates via SCCM/Intune

  • Context: The System Center Configuration Manager (SCCM) or Microsoft Intune agent executes OfficeClickToRun.exe to apply cumulative updates. This process often utilizes the RLPackAp0x packing mechanism to bundle update payloads, triggering the YARA rule on the temporary extraction folder.
  • Suggested Filter/Exclusion: Create a whitelist for processes running under C:\Program Files\Microsoft Intune Agent\ or C:\Windows\System32\ccmexec.exe. Additionally, exclude file paths containing \AppData\Local\Microsoft\Office\ClickToRun\ from the detection scope.

• Scenario: Scheduled Antivirus Definition Updates (e.g., CrowdStrike or SentinelOne)

  • Context: During nightly maintenance windows, endpoint protection agents download and unpack new definition signatures. The unpacking utility often generates a temporary executable with the RLPackAp0x signature before injecting it into memory for scanning.
  • Suggested Filter/Exclusion: Exclude processes where the parent process is C:\Program Files\CrowdStrike\fs_qr.exe or C:\Program Files\SentinelOne\SentinelHostAgent\. Add a time-based filter to suppress alerts during the defined maintenance window (e.g., 02:00 – 04:00 local time).

• Scenario: Execution of Enterprise-wide Patching Scripts via PowerShell

  • Context: IT administrators run scheduled PowerShell scripts (Update-PatchStatus.ps1) that invoke third-party patch management tools (like Ivanti or ManageEngine) which utilize RLPackAp0x to compress and