Detect CMSTP in Splunk
Adversaries may abuse CMSTP to proxy execution of malicious code. The Microsoft Connection Manager Profile Installer (CMSTP.exe) is a command-line program used to install Connection Manager service profiles. CMSTP.exe accepts an installation information file (INF) as a parameter and installs a service profile for remote access connections. Adversaries may supply CMSTP.exe with INF files infected with malicious commands to load and execute DLLs or COM scriptlets (SCT) from remote servers. This technique bypasses AppLocker since CMSTP.exe is a signed Microsoft binary. CMSTP.exe can also be abused to bypass UAC through an auto-elevated COM interface. Groups including MuddyWater, Cobalt Group, and malware like CHIMNEYSWEEP and LockBit 3.0 have used this technique.
MITRE ATT&CK
- Tactic
- Defense Evasion
- Technique
- T1218 System Binary Proxy Execution
- Sub-technique
- T1218.003 CMSTP
- Canonical reference
- https://attack.mitre.org/techniques/T1218/003/
SPL Detection Query
index=wineventlog sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational" EventCode=1
Image="*\\cmstp.exe"
| eval AutoClose=if(match(CommandLine, "(/s|/au)"), 1, 0)
| eval NoUI=if(match(CommandLine, "(/ns|/ni)"), 1, 0)
| eval HasINF=if(match(CommandLine, "\.inf"), 1, 0)
| eval SuspiciousPath=if(match(CommandLine, "(Temp|AppData|Downloads|Public|ProgramData|\\\\Users\\\\)"), 1, 0)
| eval RemoteLoad=if(match(CommandLine, "http[s]?://"), 1, 0)
| eval SuspiciousParent=if(match(ParentImage, "(cmd|powershell|wscript|cscript|mshta|winword|excel|outlook)\.exe"), 1, 0)
| eval RiskScore=AutoClose + NoUI + SuspiciousPath + RemoteLoad + SuspiciousParent
| where RiskScore > 0
| table _time, host, User, CommandLine, ParentImage, ParentCommandLine, AutoClose, NoUI, HasINF, SuspiciousPath, RemoteLoad, SuspiciousParent, RiskScore
| sort - _timeDetects malicious CMSTP.exe execution using Sysmon Event ID 1. Scores across multiple risk indicators: silent/automated flags, suspicious INF paths, remote content loading, and suspicious parent processes. Any CMSTP execution with a risk score above 0 warrants investigation.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Legitimate VPN client installations using CMSTP.exe to install Connection Manager profiles from Program Files
- Enterprise network configuration deployment using CMSTP with signed INF files from controlled paths
- IT administrators manually installing connection profiles via CMSTP for remote access setup
- Legacy Windows Remote Access Service configurations deployed via CMSTP
Other platforms for T1218.003
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1CMSTP Execution with Malicious INF File
Expected signal: Sysmon Event ID 1: cmstp.exe with /s /ns flags and Temp path in command line. Sysmon Event ID 1: calc.exe with ParentImage=cmstp.exe (child process spawned by CMSTP). Security Event ID 4688 for both processes.
- Test 2CMSTP Silent Execution from Temp Directory
Expected signal: Sysmon Event ID 1: cmstp.exe with /s flag and Temp path. The INF file creation will appear as Sysmon Event ID 11. Security Event ID 4688 for cmstp.exe process.
- Test 3CMSTP Launched from PowerShell
Expected signal: Sysmon Event ID 1: powershell.exe creating the INF file and launching cmstp.exe. Sysmon Event ID 11: INF file creation. Sysmon Event ID 1: cmstp.exe with ParentImage=powershell.exe, SuspiciousParent indicator fires.
References (7)
- https://attack.mitre.org/techniques/T1218/003/
- https://msitpros.com/?p=3960
- https://web.archive.org/web/20190316220149/http://www.endurant.io/cmstp/detecting-cmstp-enabled-code-execution-and-uac-bypass-with-sysmon/
- https://github.com/api0cradle/UltimateAppLockerByPassList
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1218.003/T1218.003.md
- https://www.fireeye.com/blog/threat-research/2018/03/suspected-iranian-influence-operation.html
- https://www.mandiant.com/resources/blog/roadsweep-august-2022
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