Detection: Single Letter Process On Endpoint

Updated Date: 2024-05-27 ID: a4214f0b-e01c-41bc-8cc4-d2b71e3056b4 Author: David Dorsey, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic detects processes with names consisting of a single letter, which is often indicative of malware or an attacker attempting to evade detection. This detection leverages data from Endpoint Detection and Response (EDR) agents, focusing on process names and command-line executions. This activity is significant because attackers use such techniques to obscure their presence and carry out malicious activities like data theft or ransomware attacks. If confirmed malicious, this behavior could lead to unauthorized access, data exfiltration, or system compromise. Immediate investigation is required to determine the legitimacy of the process.

1
2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes by Processes.dest, Processes.user, Processes.process, Processes.process_name 
3| `drop_dm_object_name(Processes)` 
4| `security_content_ctime(lastTime)` 
5| `security_content_ctime(firstTime)` 
6| eval process_name_length = len(process_name), endExe = if(substr(process_name, -4) == ".exe", 1, 0) 
7| search process_name_length=5 AND endExe=1 
8| table count, firstTime, lastTime, dest, user, process, process_name 
9| `single_letter_process_on_endpoint_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($field$)
single_letter_process_on_endpoint_filter search *
single_letter_process_on_endpoint_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
T1204 User Execution Execution
T1204.002 Malicious File Execution
KillChainPhase.INSTALLATION
NistCategory.DE_CM
Cis18Value.CIS_10
LAPSUS$
Scattered Spider
APT-C-36
APT12
APT19
APT28
APT29
APT30
APT32
APT33
APT37
APT38
APT39
Ajax Security Team
Andariel
Aoqin Dragon
BITTER
BRONZE BUTLER
BlackTech
CURIUM
Cobalt Group
Confucius
Dark Caracal
DarkHydrus
Darkhotel
Dragonfly
EXOTIC LILY
Earth Lusca
Elderwood
Ember Bear
FIN4
FIN6
FIN7
FIN8
Ferocious Kitten
Gallmaker
Gamaredon Group
Gorgon Group
HEXANE
Higaisa
Inception
IndigoZebra
Indrik Spider
Kimsuky
Lazarus Group
LazyScripter
Leviathan
Machete
Magic Hound
Malteiro
Mofang
Molerats
MuddyWater
Mustang Panda
Naikon
Nomadic Octopus
OilRig
PLATINUM
PROMETHIUM
Patchwork
RTM
Rancor
Sandworm Team
SideCopy
Sidewinder
Silence
TA2541
TA459
TA505
TA551
The White Company
Threat Group-3390
Tonto Team
Transparent Tribe
Tropic Trooper
WIRTE
Whitefly
Windshift
Wizard Spider
admin@338
menuPass

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 Notable Yes
Rule Title %name%
Rule Description %description%
Notable Event Fields user, dest
Creates Risk Event True
This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

Implementation

The detection is based on data that originates from Endpoint Detection and Response (EDR) agents. These agents are designed to provide security-related telemetry from the endpoints where the agent is installed. To implement this search, you must ingest logs that contain the process GUID, process name, and parent process. Additionally, you must ingest complete command-line executions. These logs must be processed using the appropriate Splunk Technology Add-ons that are specific to the EDR product. The logs must also be mapped to the Processes node of the Endpoint data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process.

Known False Positives

Single-letter executables are not always malicious. Investigate this activity with your normal incident-response process.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message Risk Score Impact Confidence
A suspicious process $process_name$ with single letter in host $dest$ 63 70 90
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

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: 4