Analysis by: Christopher Daniel So
 Modified by: Mark Joseph Manahan


Backdoor:Win32/Mdmbot.F (Microsoft), Backdoor.Win32.MmBot.b (Kaspersky), Win32/McRat.B trojan (Eset)


Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)


  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes


Infection Channel: Dropped by other malware, Downloaded from the Internet

This backdoor is downloaded before through a previous zero-day Java exploit, now tagged as CVE-2013-1493. This malware is also used as a payload for a zero-day Internet Explorer bug.

To get a one-glance comprehensive view of the behavior of this Backdoor, refer to the Threat Diagram shown below.

This Backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It executes then deletes itself afterward.

It executes commands from a remote malicious user, effectively compromising the affected system.


File Size: 73,728 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 01 Mar 2013
Payload: Compromises system security, Collects system information

Arrival Details

This Backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.


This Backdoor drops the following component file(s):

  • %User Profile%\AppMgmt.dll - also detected as BKDR_MDMBOT.A

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista, 7, and 8.)

Its DLL component is injected to the following process(es):

  • svchost.exe

It executes then deletes itself afterward.

Autostart Technique

This Backdoor modifies the following registry entries to ensure it automatic execution at every system startup:

ServiceDll = "%User Profile%\AppMgmt.dll"

(Note: The default value data of the said registry entry is %System%\appmgmts.dll.)

Backdoor Routine

This Backdoor executes the following commands from a remote malicious user:

  • Download and Load plugins - saved as %Temp%\{random} or %Temp%\

(Note: %Temp% is the Windows temporary folder, where it usually is C:\Windows\Temp on all Windows operating system versions.)

It connects to the following URL(s) to send and receive commands from a remote malicious user:

  • {BLOCKED}.{BLOCKED}.55.187:80
  • {BLOCKED}.{BLOCKED}.143.244:443
  • {BLOCKED}.{BLOCKED}.9.93:443

Information Theft

This Backdoor gathers the following data:

  • Computer Name
  • Admin rights
  • OS Version
  • Hostname

Other Details

This Backdoor connects to the following URL(s) to check for an Internet connection:



Minimum Scan Engine: 9.300
VSAPI OPR PATTERN File: 9.761.00
VSAPI OPR PATTERN Date: 01 Mar 2013

Step 1

Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.

Step 2

Restart in Safe Mode

[ Learn More ]

Step 3

Restore this modified registry value

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\AppMgmt\Parameters
    • From: ServiceDll = "%User Profile%\AppMgmt.dll"
      To: ServiceDll = "%System%\appmgmts.dll"

Step 4

Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_MDMBOT.A. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check this Knowledge Base page for more information.

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