Techniques
Sample rules
Windows Server Software Component GACUtil Install to GAC
- source: splunk
- technicques:
- T1505
- T1505.004
Description
The following analytic identifies the Windows SDK utility - GACUtil.exe, being utilized to add a DLL into the Global Assembly Cache (GAC). Each computer where the Common Language Runtime is installed has a machine-wide code cache called the Global Assembly Cache. The Global Assembly Cache stores assemblies specifically designated to be shared by several applications on the computer. By adding a DLL to the GAC, this allows an adversary to call it via any other means across the operating systems. As outlined by Microsoft in their blog, it is not common to see this spawning from W3WP.exe, however, in a non-development environment it may not be common at all. Note that in order to utilize GACutil.exe, The Windows SDK must be installed, this is not a native binary.
Detection logic
| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where Processes.process_name=gacutil.exe Processes.process IN ("*-i *","*/i *") by Processes.dest Processes.user Processes.parent_process_name 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)`
| `windows_server_software_component_gacutil_install_to_gac_filter`