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, specifically looking for instances where WinRAR spawns processes like “cmd.exe”, “powershell.exe”, “certutil.exe”, “mshta.exe”, or “bitsadmin.exe”. This behavior is worth identifying for a Security Operations Center (SOC) because it is indicative of a spoofing attack exploit, such as the one associated with WinRAR CVE-2023-38831. Cybercriminals exploited this vulnerability to craft ZIP archives with spoofed extensions, hiding the launch of malicious scripts within an archive. When a victim opened the specially crafted archive, it executed the malware, leading to unauthorized access to their broker accounts and enabling the cybercriminals to perform illicit financial transactions and withdraw funds. If a true positive is found, it suggests that an attacker has successfully exploited the vulnerability to execute malicious scripts, leading to unauthorized access, financial loss, and potentially the delivery of additional malicious payloads. The impact of the attack could be severe, involving financial loss, unauthorized access to sensitive accounts, and the potential for further malicious activity such as 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`