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CMSTP

The Microsoft Connection Manager Profile Installer (CMSTP.exe) is a command-line program used to install Connection Manager service profiles. [1] CMSTP.exe accepts an installation information file (INF) as a parameter and installs a service profile leveraged for remote access connections.

Adversaries may supply CMSTP.exe with INF files infected with malicious commands. [2] Similar to Regsvr32 / "Squiblydoo", CMSTP.exe may be abused to load and execute DLLs [3] and/or COM scriptlets (SCT) from remote servers. [4] [5] [6] This execution may also bypass AppLocker and other whitelisting defenses since CMSTP.exe is a legitimate, signed Microsoft application.

CMSTP.exe can also be abused to Bypass User Account Control and execute arbitrary commands from a malicious INF through an auto-elevated COM interface. [3] [5] [6]

ID: T1191

Tactic: Defense Evasion, Execution

Platform:  Windows

Permissions Required:  User

Data Sources:  Process monitoring, Process command-line parameters, Process use of network, Windows event logs

Supports Remote:  No

Defense Bypassed:  Application whitelisting, Anti-virus

Contributors:  Ye Yint Min Thu Htut, Offensive Security Team, DBS Bank, Nik Seetharaman, Palantir

Version: 1.0

Examples

NameDescription
Cobalt Group

Cobalt Group has used the command cmstp.exe /s /ns C:\Users\ADMINI~W\AppData\Local\Temp\XKNqbpzl.txt to bypass AppLocker and launch a malicious script.[7]

MuddyWater

MuddyWater has used CMSTP.exe and a malicious INF to execute its POWERSTATS payload.[8]

Mitigation

CMSTP.exe may not be necessary within a given environment (unless using it for VPN connection installation). Consider using application whitelisting configured to block execution of CMSTP.exe if it is not required for a given system or network to prevent potential misuse by adversaries. [3]

Detection

Use process monitoring to detect and analyze the execution and arguments of CMSTP.exe. Compare recent invocations of CMSTP.exe with prior history of known good arguments and loaded files to determine anomalous and potentially adversarial activity.

Sysmon events can also be used to identify potential abuses of CMSTP.exe. Detection strategy may depend on the specific adversary procedure, but potential rules include: [6]

  • To detect loading and execution of local/remote payloads - Event 1 (Process creation) where ParentImage contains CMSTP.exe and/or Event 3 (Network connection) where Image contains CMSTP.exe and DestinationIP is external.
  • To detect Bypass User Account Control via an auto-elevated COM interface - Event 10 (ProcessAccess) where CallTrace contains CMLUA.dll and/or Event 12 or 13 (RegistryEvent) where TargetObject contains CMMGR32.exe. Also monitor for events, such as the creation of processes (Sysmon Event 1), that involve auto-elevated CMSTP COM interfaces such as CMSTPLUA (3E5FC7F9-9A51-4367-9063-A120244FBEC7) and CMLUAUTIL (3E000D72-A845-4CD9-BD83-80C07C3B881F).

References