Detection: Excessive Usage of NSLOOKUP App

Updated Date: 2024-05-15 ID: 0a69fdaa-a2b8-11eb-b16d-acde48001122 Author: Teoderick Contreras, Stanislav Miskovic, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic detects excessive usage of the nslookup application, which may indicate potential DNS exfiltration attempts. It leverages Sysmon EventCode 1 to monitor process executions, specifically focusing on nslookup.exe. The detection identifies outliers by comparing the frequency of nslookup executions against a calculated threshold. This activity is significant as it can reveal attempts by malware or APT groups to exfiltrate data via DNS queries. If confirmed malicious, this behavior could allow attackers to stealthily transfer sensitive information out of the network, bypassing traditional data exfiltration defenses.

 1`sysmon` EventCode = 1 process_name = "nslookup.exe" 
 2| bucket _time span=1m 
 3| stats count as numNsLookup by dest, _time 
 4| eventstats avg(numNsLookup) as avgNsLookup, stdev(numNsLookup) as stdNsLookup, count as numSlots by dest 
 5| eval upperThreshold=(avgNsLookup + stdNsLookup *3) 
 6| eval isOutlier=if(numNsLookup > 20 and numNsLookup >= upperThreshold, 1, 0) 
 7| search isOutlier=1 
 8| `security_content_ctime(firstTime)` 
 9| `security_content_ctime(lastTime)` 
10| `excessive_usage_of_nslookup_app_filter`

Data Source

Name Platform Sourcetype Source Supported App
CrowdStrike ProcessRollup2 N/A 'crowdstrike:events:sensor' 'crowdstrike' N/A

Macros Used

Name Value
security_content_ctime convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)
excessive_usage_of_nslookup_app_filter search *
excessive_usage_of_nslookup_app_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
T1048 Exfiltration Over Alternative Protocol Exfiltration
KillChainPhase.ACTIONS_ON_OBJECTIVES
NistCategory.DE_AE
Cis18Value.CIS_10
TeamTNT

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 be ingesting logs with the process name, parent process, and command-line executions from your endpoints. If you are using Sysmon, you must have at least version 6.0.4 of the Sysmon TA. Tune and filter known instances of nslookup.exe may be used.

Known False Positives

unknown

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message Risk Score Impact Confidence
Excessive usage of nslookup.exe has been detected on $dest$. This detection is triggered as as it violates the dynamic threshold 28 40 70
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

References

Detection Testing

Test Type Status Dataset Source Sourcetype
Validation ✅ Passing N/A N/A N/A
Unit ✅ Passing Dataset XmlWinEventLog:Microsoft-Windows-Sysmon/Operational xmlwineventlog
Integration ✅ Passing Dataset XmlWinEventLog:Microsoft-Windows-Sysmon/Operational xmlwineventlog

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: 3