be aware of potential false positives - legitimate uses of winrar and the listed processes in your environment may cause benign activities to be flagged. upon triage, review the destination, user, parent process, and process name involved in the flagged activity. capture and inspect any relevant on-disk artifacts, and look for concurrent processes to identify the attack source. this approach helps analysts detect potential threats earlier and mitigate the risks.

Techniques

T1105

Sample rules

WinRAR Spawning Shell Application

source: splunk
technicques:
- T1105

Description

The following analytic detects the execution of Windows shell processes initiated by WinRAR, such as “cmd.exe”, “powershell.exe”, “certutil.exe”, “mshta.exe”, or “bitsadmin.exe”. This detection leverages data from Endpoint Detection and Response (EDR) agents, focusing on process and parent process relationships. This activity is significant because it may indicate exploitation of the WinRAR CVE-2023-38831 vulnerability, where malicious scripts are executed from spoofed ZIP archives. If confirmed malicious, this could lead to unauthorized access, financial loss, and further malicious activities like data theft or ransomware attacks.

Detection logic


| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where Processes.parent_process_name=winrar.exe `windows_shells` OR Processes.process_name IN ("certutil.exe","mshta.exe","bitsadmin.exe") by Processes.dest Processes.user Processes.parent_process_name 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)` 
| `winrar_spawning_shell_application_filter`