This detection identifies potential njRAT malware activity by analyzing network traffic patterns that match known command-and-control signatures associated with this remote access tool. Proactively hunting for these indicators in Azure Sentinel is critical to distinguish legitimate administrative sessions from stealthy lateral movements and data exfiltration attempts before they escalate into significant security incidents.
rule network_traffic_njRAT
{
meta:
author = "info@fidelissecurity.com"
descripion = "njRAT - Remote Access Trojan"
comment = "Rule to alert on network traffic indicators"
filetype = "PCAP - Network Traffic"
date = "2013-07-15"
version = "1.0"
hash1 = "92ee1fb5df21d8cfafa2b02b6a25bd3b"
hash2 ="3576d40ce18bb0349f9dfa42b8911c3a"
hash3 ="24cc5b811a7f9591e7f2cb9a818be104"
hash4 = "3ad5fded9d7fdf1c2f6102f4874b2d52"
hash5 = "a98b4c99f64315aac9dd992593830f35"
hash6 = "5fcb5282da1a2a0f053051c8da1686ef"
hash7 = "a669c0da6309a930af16381b18ba2f9d"
hash8 = "79dce17498e1997264346b162b09bde8"
hash9 = "fc96a7e27b1d3dab715b2732d5c86f80"
ref1 = "http://bit.ly/19tlf4s"
ref2 = "http://www.fidelissecurity.com/threatadvisory"
ref3 = "http://www.threatgeek.com/2013/06/fidelis-threat-advisory-1009-njrat-uncovered.html"
ref4 = "http://threatgeek.typepad.com/files/fta-1009---njrat-uncovered.pdf"
strings:
$string1 = "FM|'|'|" // File Manager
$string2 = "nd|'|'|" // File Manager
$string3 = "rn|'|'|" // Run File
$string4 = "sc~|'|'|" // Remote Desktop
$string5 = "scPK|'|'|" // Remote Desktop
$string6 = "CAM|'|'|" // Remote Cam
$string7 = "USB Video Device[endof]" // Remote Cam
$string8 = "rs|'|'|" // Reverse Shell
$string9 = "proc|'|'|" // Process Manager
$string10 = "k|'|'|" // Process Manager
$string11 = "RG|'|'|~|'|'|" // Registry Manipulation
$string12 = "kl|'|'|" // Keylogger file
$string13 = "ret|'|'|" // Get Browser Passwords
$string14 = "pl|'|'|" // Get Browser Passwords
$string15 = "lv|'|'|" // General
$string16 = "prof|'|'|~|'|'|" // Server rename
$string17 = "un|'|'|~[endof]" // Uninstall
$idle_string = "P[endof]" // Idle Connection
condition:
any of ($string*) or #idle_string > 4
}This YARA rule can be deployed in the following contexts:
This rule contains 18 string patterns in its detection logic.
Here are 4 specific false positive scenarios for the network_traffic_njRAT detection rule in an enterprise environment, along with suggested filters or exclusions:
Software Deployment via SCCM/MECM
ccmexec.exe) initiates a large outbound connection to the internal Software Update Point server during a scheduled patch deployment window. The traffic payload contains compressed installation binaries that share structural similarities with njRAT command-and-control (C2) beaconing, triggering the YARA rule due to specific header patterns in the HTTP/HTTPS stream.ccmexec.exe and the destination IP belongs to the internal “Software Distribution” subnet (e.g., 10.x.x.0/24).Endpoint Protection Telemetry Upload
csfalcon.exe) or Microsoft Defender for Endpoint (MsMpEng.exe) performs a scheduled daily telemetry upload to the cloud management portal. This involves sending encrypted logs and host inventory data that mimics the small, periodic packet sizes characteristic of njRAT C2 heartbeats, causing the YARA rule to match on the network signature.csfalcon.exe or MsMpEng.exe communicating with known vendor cloud endpoints (e.g., *.crowdstrike.com, *.microsoft.com) during standard business hours (08:00–18:00).Remote Administration via RDP Wrapper
powershell.exe) to query remote servers for compliance checks, utilizing the Remote Desktop Protocol (RDP) or WinRM. The script establishes persistent connections