Detection: Rundll32 Process Creating Exe Dll Files

Updated Date: 2024-05-22 ID: 6338266a-ee2a-11eb-bf68-acde48001122 Author: Teoderick Contreras, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic detects a rundll32 process creating executable (.exe) or dynamic link library (.dll) files. It leverages Sysmon EventCode 11 to identify instances where rundll32.exe generates these file types. This activity is significant because rundll32 is often exploited by malware, such as IcedID, to drop malicious payloads in directories like Temp, AppData, or ProgramData. If confirmed malicious, this behavior could allow an attacker to execute arbitrary code, establish persistence, or escalate privileges within the environment.

1`sysmon` EventCode=11 Image="*rundll32.exe" TargetFilename IN ("*.exe", "*.dll") 
2| stats count min(_time) as firstTime max(_time) as lastTime by Image TargetFilename Computer 
3| rename Computer as dest 
4| rename TargetFilename as file_name 
5| `security_content_ctime(firstTime)` 
6| `security_content_ctime(lastTime)` 
7| `rundll32_process_creating_exe_dll_files_filter`

Data Source

Name Platform Sourcetype Source Supported App
Sysmon EventID 11 Windows icon Windows 'xmlwineventlog' 'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational' N/A

Macros Used

Name Value
security_content_ctime convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)
rundll32_process_creating_exe_dll_files_filter search *
rundll32_process_creating_exe_dll_files_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
T1218 System Binary Proxy Execution Defense Evasion
T1218.011 Rundll32 Defense Evasion
KillChainPhase.EXPLOITAITON
NistCategory.DE_CM
Cis18Value.CIS_10
Lazarus Group
APT19
APT28
APT3
APT32
APT38
APT41
Blue Mockingbird
Carbanak
CopyKittens
FIN7
Gamaredon Group
HAFNIUM
Kimsuky
Lazarus Group
LazyScripter
Magic Hound
MuddyWater
Sandworm Team
TA505
TA551
Wizard Spider

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

To successfully implement this search, you need to be ingesting logs with the process name, TargetFilename, and eventcode 11 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 where renamed rundll32.exe may be used.

Known False Positives

unknown

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message Risk Score Impact Confidence
rundll32 process drops a file $file_name$ on host $dest$ 80 80 100
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