Detection: Remote Desktop Network Traffic

Updated Date: 2025-05-02 ID: 272b8407-842d-4b3d-bead-a704584003d3 Author: David Dorsey, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic detects unusual Remote Desktop Protocol (RDP) traffic on TCP/3389 by filtering out known RDP sources and destinations, focusing on atypical connections within the network. This detection leverages network traffic data to identify potentially unauthorized RDP access. Monitoring this activity is crucial for a SOC as unauthorized RDP access can indicate an attacker's attempt to control networked systems, leading to data theft, ransomware deployment, or further network compromise. If confirmed malicious, this activity could result in significant data breaches or complete system and network control loss.

1
2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Network_Traffic where All_Traffic.dest_port=3389 AND All_Traffic.dest_category!=common_rdp_destination AND All_Traffic.src_category!=common_rdp_source AND All_Traffic.action="allowed" by All_Traffic.src All_Traffic.dest All_Traffic.dest_port All_Traffic.dest_ip All_Traffic.dvc All_Traffic.src_ip All_Traffic.src_port All_Traffic.vendor_product 
3| `drop_dm_object_name("All_Traffic")` 
4| `security_content_ctime(firstTime)`
5| `security_content_ctime(lastTime)` 
6| `remote_desktop_network_traffic_filter`

Data Source

Name Platform Sourcetype Source
Zeek Conn N/A 'bro:conn:json' 'bro:conn:json'

Macros Used

Name Value
security_content_ctime convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)
remote_desktop_network_traffic_filter search *
remote_desktop_network_traffic_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK
+ Kill Chain Phases
+ NIST
+ CIS
- Threat Actors
ID Technique Tactic
T1021.001 Remote Desktop Protocol Lateral Movement
Exploitation
DE.AE
CIS 13

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting Value
Disabled true
Cron Schedule 0 * * * *
Earliest Time -70m@m
Latest Time -10m@m
Schedule Window auto
Creates Risk Event True
This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

Implementation

To successfully implement this search you need to identify systems that commonly originate remote desktop traffic and that commonly receive remote desktop traffic. You can use the included support search "Identify Systems Creating Remote Desktop Traffic" to identify systems that originate the traffic and the search "Identify Systems Receiving Remote Desktop Traffic" to identify systems that receive a lot of remote desktop traffic. After identifying these systems, you will need to add the "common_rdp_source" or "common_rdp_destination" category to that system depending on the usage, using the Enterprise Security Assets and Identities framework. This can be done by adding an entry in the assets.csv file located in SA-IdentityManagement/lookups.

Known False Positives

Remote Desktop may be used legitimately by users on the network.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

Remote Desktop Network Traffic Anomaly Detected from $src$ to $dest$

Risk Object Risk Object Type Risk Score Threat Objects
src system 25 dest

Detection Testing

Test Type Status Dataset Source Sourcetype
Validation ✅ Passing N/A N/A N/A
Unit ✅ Passing Dataset conn.log bro:conn:json
Integration ✅ Passing Dataset conn.log bro:conn:json

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub | Version: 11