Detect CMSTP in Microsoft Sentinel
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/
KQL Detection Query
DeviceProcessEvents
| where Timestamp > ago(24h)
| where FileName =~ "cmstp.exe"
| extend AutoClose = ProcessCommandLine has_any ("/s", "/au")
| extend NoUserInteraction = ProcessCommandLine has_any ("/ns", "/ni")
| extend HasINF = ProcessCommandLine has ".inf"
| extend SuspiciousINFPath = ProcessCommandLine has_any ("Temp", "AppData", "Downloads", "Public", "ProgramData", "\\Users\\")
| extend RemoteLoad = ProcessCommandLine has_any ("http://", "https://")
| extend SuspiciousParent = InitiatingProcessFileName has_any ("cmd.exe", "powershell.exe", "wscript.exe", "cscript.exe", "mshta.exe", "winword.exe", "excel.exe", "outlook.exe")
| project Timestamp, DeviceName, AccountName, ProcessCommandLine, InitiatingProcessFileName,
InitiatingProcessCommandLine, AutoClose, NoUserInteraction, HasINF,
SuspiciousINFPath, RemoteLoad, SuspiciousParent
| sort by Timestamp descDetects CMSTP.exe abuse by identifying non-interactive execution flags (/s, /ns, /ni, /au) used in adversarial contexts, INF files loaded from user-writable paths, remote INF/SCT loading via HTTP, and suspicious parent processes. Legitimate CMSTP usage by VPN clients uses fixed paths and is typically user-initiated.
Data Sources
Required Tables
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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