Detection: Detect Regasm with Network Connection

Updated Date: 2024-08-14 ID: 07921114-6db4-4e2e-ae58-3ea8a52ae93f Author: Michael Haag, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic detects the execution of regasm.exe establishing a network connection to a public IP address, excluding private IP ranges. This detection leverages Sysmon EventID 3 logs to identify such behavior. This activity is significant as regasm.exe is a legitimate Microsoft-signed binary that can be exploited to bypass application control mechanisms. If confirmed malicious, this behavior could indicate an adversary's attempt to establish a remote Command and Control (C2) channel, potentially leading to privilege escalation and further malicious actions within the environment.

1`sysmon` EventID=3 dest_ip!=10.0.0.0/8 dest_ip!=172.16.0.0/12 dest_ip!=192.168.0.0/16 process_name=regasm.exe  
2| stats count min(_time) as firstTime max(_time) as lastTime by dest, user, process_name, src_ip, dest_ip 
3| `security_content_ctime(firstTime)` 
4| `security_content_ctime(lastTime)` 
5| `detect_regasm_with_network_connection_filter`

Data Source

Name Platform Sourcetype Source Supported App
Sysmon EventID 3 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($field$)
detect_regasm_with_network_connection_filter search *
detect_regasm_with_network_connection_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
T1218.009 Regsvcs/Regasm Defense Evasion
KillChainPhase.EXPLOITAITON
NistCategory.DE_CM
Cis18Value.CIS_10
Lazarus Group

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, 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.

Known False Positives

Although unlikely, limited instances of regasm.exe with a network connection may cause a false positive. Filter based endpoint usage, command line arguments, or process lineage.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message Risk Score Impact Confidence
An instance of $process_name$ contacting a remote destination was identified on endpoint $dest$ by user $user$. This behavior is not normal for $process_name$. 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: 5