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Malicious Software Encyclopedia: Backdoor:Win32/Rbot.MA

Published: August 16, 2005

Backdoor:Win32/Rbot.MA is a backdoor Trojan that targets computers running certain versions of Microsoft Windows. The Trojan connects to an IRC server from the infected computer to receive commands from attackers. Such commands may copy the Trojan to other computers through network shares with weak passwords, through backdoor ports opened by other malicious software, or through the Windows Plug-and-Play vulnerability described in Microsoft Security Bulletin MS05-039.

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Glossary Terms

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Trojan horse

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virus

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worm

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On This Page
Threat OverviewThreat Overview
Related Security BulletinsRelated Security Bulletins
Technical AnalysisTechnical Analysis
How to Prevent InfectionHow to Prevent Infection
How to Tell If Your Computer Is InfectedHow to Tell If Your Computer Is Infected
How to Recover from InfectionHow to Recover from Infection
Transmission MethodsTransmission Methods
Payload InformationPayload Information
Modified Registry EntriesModified Registry Entries
Changed ServicesChanged Services
Affected PortsAffected Ports
Dropped FilesDropped Files

Threat Overview

Class/typeTrojan - Backdoor
DiscoveredAugust 3, 2009
CirculatingYes
Affected operating systemsWindows 95
Windows 2000
Windows XP
Windows Server 2003
Windows ME
Windows 98
Affected software Not specified
Infection ratingLow
Recovery difficultyModerate
Damage ratingMedium
Transmission ratingLow

Related Security Bulletins

The following Microsoft Security bulletins are related to this issue:

  • MS05-039 - Vulnerability in Plug and Play Could Allow Remote Code Execution and Elevation of Privilege (899588)

    • Technical Analysis

    When Backdoor:Win32/Rbot.MA runs, it can take the following actions:
    • Copy itself as a new file to <system folder>\pnpsrv.exe.
    • Run the Trojan copy, <system folder>\pnpsrv.exe, which can then take the following actions:
      • Create the value: Windows PNP Server
        with data: pnpsrv.exe
        in each of the following registry keys:
        HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
        HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
        HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices
        HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices
        HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\OLE
        HKEY_CURRENT_USER\SOFTWARE\Microsoft\OLE
        HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa
        HKEY_CURRENT_USER\SYSTEM\CurrentControlSet\Control\Lsa
      • Open and monitor TCP port 113.
      • Connect to a specific IRC server and channel to enable attackers to perform functions such as the following:
        • Gather data, including system information, file information, and Windows clipboard contents.
        • Start a command shell and run commands.
        • Conduct denial of service (DoS) attacks against certain Web sites.
        • Visit certain Web sites and download files.
        • Copy the Trojan to other computers by the following means:
          • Through backdoor ports opened by other families of malicious software.
          • Through network shares with weak user names and passwords.
          • Using a command shell that it creates on a remote computer. It creates the shell by exploiting the Windows Plug and Play vulnerability described in Microsoft Security Bulletin MS05-039. The Trojan uses the command shell to copy itself to the remote computer and then creates a task to run the copy there.

    How to Prevent Infection

    Follow these steps to help prevent infection on your system:
    • Enable a firewall on your computer.
    • Get the latest computer updates.
    • Use up-to-date antivirus software.
    • Use strong passwords.
    • Remove unneeded network shares.

    Enable a firewall on your computer

    Use a third-party firewall product or turn on the Microsoft Windows XP Internet Connection Firewall.
    To turn on the Internet Connection Firewall in Windows XP
    1. Click Start, and click Control Panel.
    2. Click Network and Internet Connections, and click Network Connections. If you do not see Network and Internet Connections, click Switch to Category View.
    3. Highlight a connection that you want to help protect, and click Change settings of this connection.
    4. Click Advanced, and select Protect my computer and network by limiting or preventing access to this computer from the Internet.
    5. Click OK.

    Get the latest computer updates

    Updates help protect your computer from viruses, worms, and other threats as they are discovered. You can use the Automatic Updates feature in Microsoft Windows XP to automatically download future Microsoft security updates while your computer is on and connected to the Internet.
    To turn on Automatic Updates in Windows XP
    1. Click Start, and click Control Panel.
    2. Click Performance and Maintenance. If you do not see Performance and Maintenance, click Switch to Category View.
    3. Click System.
    4. Click Automatic Updates, and select Keep my computer up to date.
    5. Select a setting. Microsoft recommends selecting Automatically download the updates, and install them on the schedule that I specify and setting a regular update time.
    6. If you choose to have Automatic Updates notify you in step 5, you will see a notification balloon when new downloads are available to install. Click the notification balloon to review and install updates.

    Use up-to-date antivirus software

    Most antivirus software can detect and prevent infection by known malicious software. You should always run antivirus software on your computer that is updated with the latest signature files to automatically help protect you from infection. If you don't have antivirus software installed, you can get it from one of several companies. For more information, see http://www.microsoft.com/athome/security/downloads/default.mspx  

    Use strong passwords

    A strong password has at least eight characters and includes a combination of letters, numbers, and symbols. It is easy for you to remember, but difficult for others to guess. Weak passwords include any words in the dictionary, names, dates, consecutive letters or numbers, common words with symbol substitutions (for example, p@ssw0rd), and so on.

    Remove unneeded network shares

    Malicious software can often spread over network shares. Remove unneeded network shares that are mapped to your computer.
    To remove network shares in Windows XP
    1. On the Start menu, click My Computer.
    2. On the Tools menu, click Disconnect Network Drives…
    3. In the Disconnect Network Drives dialog box, click the drives to disconnect and click OK.

    How to Tell If Your Computer Is Infected

    There are no readily apparent indications that your computer is infected with Backdoor:Win32/Rbot.MA. However, your computer may be infected by this Trojan if you notice any of the following symptoms:
    • Presence of the file <system folder>\pnpsrv.exe.
    • Presence of value: Windows PNP Server
      with data: pnpsrv.exe
      in the following registry keys:
      HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
      HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
      HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices
      HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices
      HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\OLE
      HKEY_CURRENT_USER\SOFTWARE\Microsoft\OLE
      HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa
      HKEY_CURRENT_USER\SYSTEM\CurrentControlSet\Control\Lsa
    • The Processes tab in Windows Task Manager shows that process pnpsrv.exe is running.
    • The executable file pnpsrv.exe is running as a service.

    How to Recover from Infection

    Automatic Recovery
    To attempt to automatically remove this threat, run one of the following removal tools:

    Manual Recovery

    To manually recover from infection by Backdoor:Win32/Rbot.MA, follow these steps:
    1. Install Windows security update MS05-039.
    2. Disconnect from the Internet.
    3. Restart your computer in safe mode.
    4. End the Trojan process.
    5. Delete the Trojan file from your computer.
    6. Delete the Trojan registry entries.
    7. Restart your computer.
    8. Take steps to prevent re-infection.

    Install Windows security update MS05-039

    To install MS05-039 using Windows Update
    1. Go to the Windows Update Web site at windowsupdate.microsoft.com.
    2. On the Windows Update site, click Scan for Updates. Windows Update scans your computer and returns a list of critical updates, including service packs.
    3. In the Pick updates to install list, click Critical Updates and Service Packs. Windows Update creates a list of the updates appropriate for your computer, including MS05-039 if it is not installed. Critical updates are selected for download automatically.
    4. Click Review and install updates, and then click Install Now. You may need to restart your computer after installing the updates.

    Disconnect from the Internet

    To help ensure that your computer is not actively infecting other computers, disconnect it from the Internet before proceeding. Print this Web page or save a copy on your computer; then unplug your network cable and disable your wireless connection. You can reconnect to the Internet after completing these steps.

    Restart your computer in safe mode

    To start your the computer in safe mode
    1. Remove all floppy disks and CDs from your computer, and then restart your computer.
    2. When prompted, press F8. If Windows starts without displaying the Please select the operating system to start menu, restart your computer. Press F8 after the firmware POST process completes, but before Windows displays graphical output.
    3. From the Windows Advanced Options menu, select a safe mode option.

    End the Trojan process

    Ending the Trojan process will help stop your computer from infecting other computers as well as resolve the crashing, rebooting, and performance degradation issues caused by the Trojan.
    To end the Trojan process
    1. Press CTRL+ALT+DEL once and click Task Manager.
    2. Click Processes and click Image Name to sort the running processes by name.
    3. Select the process pnpsrv.exe, and click End Process.

    Delete the Trojan file from your computer

    To delete the Trojan file from your computer
    1. Click Start, and click Run.
    2. In the Open field, type the name of the system folder, for example C:\Windows\System32 
    3. Click OK.
    4. Click Name to sort files by name.
    5. Delete the file pnpsrv.exe if it is in the list.
    6. On the Desktop, right-click the Recycle Bin and click Empty Recycle Bin.
    7. Click Yes to confirm the deletion.
    If deleting pnpsrv.exe fails, follow these steps to verify that the file is not running:
    1. Press CTRL+ALT+DEL once and click Task Manager.
    2. Click Processes and click Image Name to sort the running processes by name.
    3. Confirm that the file is not in the list.

    Delete the Trojan registry entries

    Backdoor:Win32/Rbot.MA creates numerous entries in the Windows registry. These entries should be deleted.
    To delete the Trojan registry entries
    1. On the Start menu, click Run.
    2. Type regedit and click OK.
    3. In the left pane, navigate to the key:
      HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    4. In the right pane, right-click the following value, if it exists: Windows PNP Server
    5. Click Delete and click Yes to delete the value.
    6. Repeat steps 3 through 5 for each of the following registry keys:
      HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
      HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices
      HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices
      HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\OLE
      HKEY_CURRENT_USER\SOFTWARE\Microsoft\OLE
      HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa
      HKEY_CURRENT_USER\SYSTEM\CurrentControlSet\Control\Lsa
    7. Close the Registry Editor.

    Restart your computer

    To restart your computer
    1. On the Start menu, click Shut Down.
    2. Select Restart from the drop-down list and click OK.

    Take steps to prevent re-infection

    Do not reconnect your computer to the Internet until the computer is protected from re-infection. See the "Preventing Infection" section for more information.

    Transmission Methods

    MethodDescription
    Exploits VulnerabilityCan spread by exploiting the Windows Plug and Play buffer overflow vulnerability (MS05-039).
    Network ScanningCan spread through backdoor ports opened by other malicious software.
    Network SharesCan copy itself to writeable network shares with weak user names and passwords.

    Payload Information

    Payload typeTriggerDescription
    Compromises Security
    Execution
    Connects to a specific IRC server and channel to enable attackers to control the computer.
    Creates files
    Execution
    Creates a copy of itself at <system folder>\pnpsrv.exe.

    Modified Registry Entries

    Added registry entries
    KeyHKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    Value nameWindows PNP Server [String]
    KeyHKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices
    Value nameWindows PNP Server [String]
    KeyHKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\OLE
    Value nameWindows PNP Server [String]
    KeyHKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa
    Value nameWindows PNP Server [String]
    KeyHKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    Value nameWindows PNP Server [String]
    KeyHKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices
    Value nameWindows PNP Server [String]
    KeyHKEY_CURRENT_USER\SOFTWARE\Microsoft\OLE
    Value nameWindows PNP Server [String]
    KeyHKEY_CURRENT_USER\SYSTEM\CurrentControlSet\Control\Lsa
    Value nameWindows PNP Server [String]
    Changed registry entries
    KeyHKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    Value nameWindows PNP Server [String]
    Old value
    New valuepnpsrv.exe [String]
    KeyHKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices
    Value nameWindows PNP Server [String]
    Old value
    New valuepnpsrv.exe [String]
    KeyHKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\OLE
    Value nameWindows PNP Server [String]
    Old value
    New valuepnpsrv.exe [String]
    KeyHKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa
    Value nameWindows PNP Server [String]
    Old value
    New valuepnpsrv.exe [String]
    KeyHKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    Value nameWindows PNP Server [String]
    Old value
    New valuepnpsrv.exe [String]
    KeyHKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices
    Value nameWindows PNP Server [String]
    Old value
    New valuepnpsrv.exe [String]
    KeyHKEY_CURRENT_USER\SOFTWARE\Microsoft\OLE
    Value nameWindows PNP Server [String]
    Old value
    New valuepnpsrv.exe [String]
    KeyHKEY_CURRENT_USER\SYSTEM\CurrentControlSet\Control\Lsa
    Value nameWindows PNP Server [String]
    Old value
    New valuepnpsrv.exe [String]

    Changed Services

    Added servicespnpsrv.exe

    Affected Ports

    ProtocolPort number
    TCP113

    Dropped Files

    Path<system folder>\pnpsrv.exe

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