Signed Binary Proxy Execution: CMSTP

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. [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 application control defenses since CMSTP.exe is a legitimate, signed Microsoft application.

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

ID: T1218.003
Sub-technique of:  T1218
Tactic: Defense Evasion
Platforms: Windows
Permissions Required: User
Data Sources: Process command-line parameters, Process monitoring, Process use of network, Windows event logs
Defense Bypassed: Anti-virus, Application control
Contributors: Nik Seetharaman, Palantir; Ye Yint Min Thu Htut, Offensive Security Team, DBS Bank
Version: 1.0
Created: 23 January 2020
Last Modified: 20 June 2020

Procedure Examples

Name Description
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][8][9]

MuddyWater

MuddyWater has used CMSTP.exe and a malicious INF to execute its POWERSTATS payload.[10]

Mitigations

Mitigation Description
Disable or Remove Feature or Program

CMSTP.exe may not be necessary within a given environment (unless using it for VPN connection installation).

Execution Prevention

Consider using application control configured to block execution of CMSTP.exe if it is not required for a given system or network to prevent potential misuse by adversaries.

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 Access 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