Analytics Story: Signed Binary Proxy Execution InstallUtil

Description

Adversaries may use InstallUtil to proxy execution of code through a trusted Windows utility.

Why it matters

InstallUtil is a command-line utility that allows for installation and uninstallation of resources by executing specific installer components specified in .NET binaries. InstallUtil is digitally signed by Microsoft and located in the .NET directories on a Windows system: C:\Windows\Microsoft.NET\Framework\v\InstallUtil.exe and C:\Windows\Microsoft.NET\Framework64\v\InstallUtil.exe. There are multiple ways to instantiate InstallUtil and they are all outlined within Atomic Red Team - https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1218.004/T1218.004.md. Two specific ways may be used and that includes invoking via installer assembly class constructor through .NET and via InstallUtil.exe. Typically, adversaries will utilize the most commonly found way to invoke via InstallUtil Uninstall method. Note that parallel processes, and parent process, play a role in how InstallUtil is being used. In particular, a developer using InstallUtil will spawn from VisualStudio. Adversaries, will spawn from non-standard processes like Explorer.exe, cmd.exe or PowerShell.exe. It's important to review the command-line to identify the DLL being loaded. Parallel processes may also include csc.exe being used to compile a local .cs file. This file will be the input to the output. Developers usually do not build direct on the command shell, therefore this should raise suspicion.

Detections

Data Sources

Name ▲▼	Platform ▲▼	Sourcetype ▲▼	Source ▲▼
CrowdStrike ProcessRollup2	N/A	crowdstrike:events:sensor	crowdstrike
Sysmon EventID 1	Windows	xmlwineventlog	XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
Sysmon EventID 3	Windows	xmlwineventlog	XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
Sysmon EventID 7	Windows	xmlwineventlog	XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
Windows Event Log Security 4688	Windows	xmlwineventlog	XmlWinEventLog:Security

References

• https://attack.mitre.org/techniques/T1218/004/
• https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1218.004/T1218.004.md

Source: GitHub | Version: 1