This hunt targets adversaries deploying the PolishBankRAT malware by identifying its unique XOR decoding loop within the srservice process to confirm active payload execution. Proactively hunting for this signature in Azure Sentinel is critical because it enables early detection of banking sector threats before they establish persistence or exfiltrate sensitive financial data.
rule PolishBankRAT_srservice_xorloop
{
meta:
author = "Booz Allen Hamilton Dark Labs"
description = "Finds the custom xor decode loop for <PolishBankRAT_srservice>"
strings:
$loop = { 48 8B CD E8 60 FF FF FF 48 FF C3 32 44 1E FF 48 FF CF 88 43 FF }
condition:
(uint16(0) == 0x5A4D and uint32(uint32(0x3C)) == 0x00004550) and $loop
}
This YARA rule can be deployed in the following contexts:
This rule contains 1 string patterns in its detection logic.
Here are 4 specific false positive scenarios for the PolishBankRAT_srservice XOR decode detection rule in an enterprise environment:
Scenario: Scheduled Antivirus Database Updates via Custom Agent Scripts
Update-DefenderDB.ps) to orchestrate local antivirus definitions. This script includes a legacy code block that performs XOR decoding on compressed configuration manifests before applying them, mimicking the specific loop signature of the PolishBankRAT.NT SERVICE\AntivirusAgent) or filter out execution paths located in the dedicated update directory (e.g., C:\ProgramData\EnterpriseAV\Updates\Scripts\*).Scenario: Legacy ERP Data Migration Batch Jobs
DtsExec.exe or the specific command line argument containing -PackagePath "C:\ETL\Jobs\FinancialMigration.dtsx".Scenario: Internal DevOps Artifact Signing and Verification
artifactsign to verify digital signatures of deployment packages. This tool implements an XOR decoding loop as part of its checksum validation mechanism for encrypted container images, which is indistinguishable from the RAT’s behavior at the byte-code level.
Filter/Exclusion: Whitelist the executable hash (SHA-256) of