xRAT

Hunt Hypothesis

This hypothesis posits that adversaries are deploying the xRAT remote access trojan to establish persistent footholds and exfiltrate sensitive data from endpoints within the Azure environment. The SOC team should proactively hunt for this behavior using YARA-based detection in Sentinel to identify early-stage infections before they escalate into significant data breaches or lateral movement campaigns.

YARA Rule

rule xRAT : RAT
{
    meta:
        author = " Kevin Breen <[email protected]>"
        date = "2014/04"
        ref = "http://malwareconfig.com/stats/xRat"
        maltype = "Remote Access Trojan"
        filetype = "exe"

    strings:
        $v1a = "DecodeProductKey"
        $v1b = "StartHTTPFlood"
        $v1c = "CodeKey"
        $v1d = "MESSAGEBOX"
        $v1e = "GetFilezillaPasswords"
        $v1f = "DataIn"
        $v1g = "UDPzSockets"
        $v1h = {52 00 54 00 5F 00 52 00 43 00 44 00 41 00 54 00 41}

        $v2a = "<URL>k__BackingField"
        $v2b = "<RunHidden>k__BackingField"
        $v2c = "DownloadAndExecute"
        $v2d = "-CHECK & PING -n 2 127.0.0.1 & EXIT" wide
        $v2e = "england.png" wide
        $v2f = "Showed Messagebox" wide
    condition:
        all of ($v1*) or all of ($v2*)
}

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 14 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the xRAT detection rule in an enterprise environment, including suggested filters and exclusions:

• Endpoint Security Agent Self-Updates

  • Scenario: The xRAT YARA signature often matches the behavior of legitimate Endpoint Detection and Response (EDR) agents updating their own definition databases or core modules. Specifically, when CrowdStrike Falcon or Microsoft Defender for Endpoint performs a background service update (MsMpEng.exe or csagent.exe), it may spawn child processes that mimic xRAT’s memory injection or network beaconing patterns.
  • Filter/Exclusion: Exclude the specific process names of known EDR agents (e.g., MsMpEng.exe, csagent.exe, SentinelOneAgent.exe) and their associated update service paths located in C:\Program Files\Windows Defender or C:\ProgramData\CrowdStrike.

• Scheduled Software Deployment via SCCM/Intune

  • Scenario: Enterprise-wide software deployments managed by Microsoft Endpoint Configuration Manager (SCCM) or Microsoft Intune frequently trigger this rule. During a scheduled maintenance window, the deployment engine (ccmexec.exe) installs remote management tools that establish persistent connections and inject scripts into user sessions, which xRAT flags as potential command-and-control activity.
  • Filter/Exclusion: Create an exclusion for processes launched by ccmexec.exe or IntuneManagementExtension.exe during defined business hours (e.g., 08:00–17:00) and specifically target the installation paths under C:\Program Files\Microsoft Intune Management Extension.

• Remote Desktop Administration Sessions

  • Scenario: When IT administrators utilize Microsoft Remote Desktop Services (RDS) or third-party tools like TeamViewer for