---
title: "Detect Regasm with no Command Line Arguments"
excerpt: "Signed Binary Proxy Execution, Regsvcs/Regasm"
categories:
  - Endpoint
last_modified_at: 2021-09-20
toc: true
toc_label: ""
tags:
  - Signed Binary Proxy Execution
  - Defense Evasion
  - Regsvcs/Regasm
  - Defense Evasion
  - Splunk Enterprise
  - Splunk Enterprise Security
  - Splunk Cloud
  - Endpoint
---



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#### Description

The following analytic identifies regasm.exe with no command line arguments. This particular behavior occurs when another process injects into regasm.exe, no command line arguments will be present. During investigation, identify any network connections and parallel processes. Identify any suspicious module loads related to credential dumping or file writes. Regasm.exe are natively found in `C:\Windows\Microsoft.NET\Framework\v*\regasm|regsvcs.exe` and `C:\Windows\Microsoft.NET\Framework64\v*\regasm|regsvcs.exe`.

- **Type**: [TTP](https://github.com/splunk/security_content/wiki/Detection-Analytic-Types)
- **Product**: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- **Datamodel**: [Endpoint](https://docs.splunk.com/Documentation/CIM/latest/User/Endpoint)
- **Last Updated**: 2021-09-20
- **Author**: Michael Haag, Splunk
- **ID**: c3bc1430-04e7-4178-835f-047d8e6e97df


#### [ATT&CK](https://attack.mitre.org/)

| ID             | Technique        |  Tactic             |
| -------------- | ---------------- |-------------------- |
| [T1218](https://attack.mitre.org/techniques/T1218/) | Signed Binary Proxy Execution | Defense Evasion |

| [T1218.009](https://attack.mitre.org/techniques/T1218/009/) | Regsvcs/Regasm | Defense Evasion |

#### Search

```

| tstats `security_content_summariesonly` count FROM datamodel=Endpoint.Processes where `process_regasm` by _time span=1h  Processes.process_id Processes.process_name Processes.dest Processes.process_path Processes.process Processes.parent_process_name 
| `drop_dm_object_name(Processes)` 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| regex process="(regasm\.exe.{0,4}$)" 
| `detect_regasm_with_no_command_line_arguments_filter`
```

#### Macros
The SPL above uses the following Macros:
* [process_regasm](https://github.com/splunk/security_content/blob/develop/macros/process_regasm.yml)
* [security_content_ctime](https://github.com/splunk/security_content/blob/develop/macros/security_content_ctime.yml)
* [security_content_summariesonly](https://github.com/splunk/security_content/blob/develop/macros/security_content_summariesonly.yml)

Note that `detect_regasm_with_no_command_line_arguments_filter` is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

#### Required field
* _time
* Processes.dest
* Processes.user
* Processes.parent_process_name
* Processes.parent_process
* Processes.original_file_name
* Processes.process_name
* Processes.process
* Processes.process_id
* Processes.parent_process_path
* Processes.process_path
* Processes.parent_process_id


#### How To Implement
To successfully implement this search you need to be ingesting information on process that include the name of the process responsible for the changes from your endpoints into the `Endpoint` datamodel in the `Processes` node. In addition, confirm the latest CIM App 4.20 or higher is installed and the latest TA for the endpoint product.

#### Known False Positives
Although unlikely, limited instances of regasm.exe or may cause a false positive. Filter based endpoint usage, command line arguments, or process lineage.

#### Associated Analytic story
* [Suspicious Regsvcs Regasm Activity](/stories/suspicious_regsvcs_regasm_activity)


#### Kill Chain Phase
* Actions on Objectives



#### RBA

| Risk Score  | Impact      | Confidence   | Message      |
| ----------- | ----------- |--------------|--------------|
| 49.0 | 70 | 70 | The process $process_name$ was spawned by $parent_process_name$ without any command-line arguments on $dest$ by $user$. |


Note that risk score is calculated base on the following formula: `(Impact * Confidence)/100`



#### Reference

* [https://attack.mitre.org/techniques/T1218/009/](https://attack.mitre.org/techniques/T1218/009/)
* [https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1218.009/T1218.009.md](https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1218.009/T1218.009.md)
* [https://lolbas-project.github.io/lolbas/Binaries/Regasm/](https://lolbas-project.github.io/lolbas/Binaries/Regasm/)



#### Test Dataset
Replay any dataset to Splunk Enterprise by using our [`replay.py`](https://github.com/splunk/attack_data#using-replaypy) tool or the [UI](https://github.com/splunk/attack_data#using-ui).
Alternatively you can replay a dataset into a [Splunk Attack Range](https://github.com/splunk/attack_range#replay-dumps-into-attack-range-splunk-server)

* [https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1218.009/atomic_red_team/windows-sysmon.log](https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1218.009/atomic_red_team/windows-sysmon.log)



[*source*](https://github.com/splunk/security_content/tree/develop/detections/endpoint/detect_regasm_with_no_command_line_arguments.yml) \| *version*: **2**