Anomalous usage of 7zip

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Description

The following detection identifies a 7z.exe spawned from Rundll32.exe or Dllhost.exe. It is assumed that the adversary has brought in 7z.exe and 7z.dll. It has been observed where an adversary will rename 7z.exe. Additional coverage may be required to identify the behavior of renamed instances of 7z.exe. During triage, identify the source of injection into Rundll32.exe or Dllhost.exe. Capture any files written to disk and analyze as needed. Review parallel processes for additional behaviors. Typically, archiving files will result in exfiltration.

• Type: Anomaly
• Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
• Datamodel: Endpoint
• Last Updated: 2021-04-22
• Author: Michael Haag, Teoderick Contreras, Splunk
• ID: 9364ee8e-a39a-11eb-8f1d-acde48001122

Annotations

ATT&CK

ATT&CK

ID	Technique	Tactic
T1560.001	Archive via Utility	Collection

T1560

Archive Collected Data

Collection

Kill Chain Phase

• Exploitation

NIST

CIS20

CVE

Search

| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where Processes.parent_process_name IN ("rundll32.exe", "dllhost.exe") Processes.process_name=*7z* by Processes.dest Processes.user Processes.parent_process Processes.process_name Processes.process Processes.process_id Processes.parent_process_id 
| `drop_dm_object_name(Processes)` 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)`
| `anomalous_usage_of_7zip_filter`

Macros

The SPL above uses the following Macros:

• security_content_summariesonly
• security_content_ctime

anomalous_usage_of_7zip_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Supported Add-on (TA)

List of Splunk Add-on’s tested to work with the analytic.

• Splunk Add-on for Sysmon

Required fields

List of fields required to use this analytic.

• _time
• Processes.process_name
• Processes.process
• Processes.dest
• Processes.user
• Processes.parent_process_name
• Processes.process_name
• Processes.parent_process
• Processes.process_id
• 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.

Known False Positives

False positives should be limited as this behavior is not normal for rundll32.exe or dllhost.exe to spawn and run 7zip.

Associated Analytic Story

• Cobalt Strike
• NOBELIUM Group

RBA

Risk Score	Impact	Confidence	Message
64.0	80	80	An instance of $parent_process_name$ spawning $process_name$ was identified on endpoint $dest$ by user $user$. This behavior is indicative of suspicious loading of 7zip.

The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

Reference

• https://attack.mitre.org/techniques/T1560/001/
• https://www.microsoft.com/security/blog/2021/01/20/deep-dive-into-the-solorigate-second-stage-activation-from-sunburst-to-teardrop-and-raindrop/
• https://thedfirreport.com/2021/01/31/bazar-no-ryuk/

Test Dataset

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

• https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1560.001/archive_utility/windows-sysmon.log

source | version: 1