---
title: "Detect Regsvr32 Application Control Bypass"
excerpt: "Signed Binary Proxy Execution, Regsvr32"
categories:
  - Endpoint
last_modified_at: 2021-01-28
toc: true
toc_label: ""
tags:
  - Signed Binary Proxy Execution
  - Defense Evasion
  - Regsvr32
  - Defense Evasion
  - Splunk Enterprise
  - Splunk Enterprise Security
  - Splunk Cloud
  - Endpoint
---



[Try in Splunk Security Cloud](https://www.splunk.com/en_us/cyber-security.html){: .btn .btn--success}

#### Description

Adversaries may abuse Regsvr32.exe to proxy execution of malicious code. Regsvr32.exe is a command-line program used to register and unregister object linking and embedding controls, including dynamic link libraries (DLLs), on Windows systems. Regsvr32.exe is also a Microsoft signed binary.This variation of the technique is often referred to as a &#34;Squiblydoo&#34; attack. \
Upon investigating, look for network connections to remote destinations (internal or external). Be cautious to modify the query to look for &#34;scrobj.dll&#34;, the &#34;.dll&#34; is not required to load scrobj. &#34;scrobj.dll&#34; will be loaded by &#34;regsvr32.exe&#34; upon execution. 

- **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**: 2021-01-28
- **Author**: Michael Haag, Splunk
- **ID**: 070e9b80-6252-11eb-ae93-0242ac130002


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

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

| [T1218.010](https://attack.mitre.org/techniques/T1218/010/) | Regsvr32 | Defense Evasion |

#### Search

```

| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where `process_regsvr32` Processes.process=*scrobj* by Processes.dest Processes.user Processes.parent_process Processes.process_name Processes.process Processes.original_file_name Processes.process_id Processes.parent_process_id 
| `drop_dm_object_name(Processes)` 
| `security_content_ctime(firstTime)`
| `security_content_ctime(lastTime)` 
| `detect_regsvr32_application_control_bypass_filter`
```

#### Macros
The SPL above uses the following Macros:
* [process_regsvr32](https://github.com/splunk/security_content/blob/develop/macros/process_regsvr32.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_regsvr32_application_control_bypass_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
Limited false positives related to third party software registering .DLL&#39;s.

#### Associated Analytic story
* [Suspicious Regsvr32 Activity](/stories/suspicious_regsvr32_activity)
* [Cobalt Strike](/stories/cobalt_strike)


#### Kill Chain Phase
* Actions on Objectives



#### RBA

| Risk Score  | Impact      | Confidence   | Message      |
| ----------- | ----------- |--------------|--------------|
| 80.0 | 80 | 100 | An instance of $parent_process_name$ spawning $process_name$ in an attempt to bypass detection and preventative controls was identified on endpoint $dest$ by user $user$. |


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



#### Reference

* [https://attack.mitre.org/techniques/T1218/010/](https://attack.mitre.org/techniques/T1218/010/)
* [https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1218.010/T1218.010.md](https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1218.010/T1218.010.md)
* [https://lolbas-project.github.io/lolbas/Binaries/Regsvr32/](https://lolbas-project.github.io/lolbas/Binaries/Regsvr32/)
* [https://support.microsoft.com/en-us/topic/how-to-use-the-regsvr32-tool-and-troubleshoot-regsvr32-error-messages-a98d960a-7392-e6fe-d90a-3f4e0cb543e5](https://support.microsoft.com/en-us/topic/how-to-use-the-regsvr32-tool-and-troubleshoot-regsvr32-error-messages-a98d960a-7392-e6fe-d90a-3f4e0cb543e5)



#### 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/T1218.010/atomic_red_team/windows-sysmon.log](https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1218.010/atomic_red_team/windows-sysmon.log)



[*source*](https://github.com/splunk/security_content/tree/develop/detections/endpoint/detect_regsvr32_application_control_bypass.yml) \| *version*: **2**