Backdoor:Win32/Simda.gen!A

Backdoor:Win32/Simda.gen!A is a backdoor trojan that allows remote access and control of an affected computer.

Installation

When executed, the malware:

• Checks if the trojan is running from the <system folder>. If it isn't running from the system folder, Backdoor:Win32/Simda.gen!A copies itself as <system folder>\<random_number>.exe
• Modifies the following registry entry to execute its copy at Windows start:
  
  In subkey: HKLM\Software\Microsoft\Windows NT\Currentversion\Winlogon
  Sets value: "userinit"
  With data: "<system folder>\userinit.exe, <system folder>\<random_number>.exe"
• Injects code to the process “svchost.exe”
• Deletes the original executable

Note: <system folder> refers to a variable location that is determined by the malware by querying the Operating System. The default installation location for the System folder for Windows 2000 and NT is C:\Winnt\System32; and for XP, Vista, and 7 is C:\Windows\System32.

Payload

Downloads and executes arbitrary files

Backdoor:Win32/Simda.gen!A connects to a remote host and provides information regarding the newly infected computer.

It then receives the configuration information on where to download additional files, and other locations from which to download additional configuration files. Downloaded files are written to the %TEMP% folder, for example C:\Users\<user name>\AppData\Local\Temp. These files may include additional malware.

In the wild, we have observed the following domains being contacted for this purpose:

• gusssiss.com
• orlikssss.com
• asterixsss.com

Modifies security settings

Backdoor:Win32/Simda.gen!A uses various techniques in an attempt to elevate its privilege. It attempts to log on as Administrator (if the user isn't Admin already) using a list of passwords:

• help
• stone
• server
• pass
• idontknow
• administrator
• admin
• 666666
• 111
• 12345678
• 1234
• soccer
• abc123
• password1
• football1
• fuckyou
• monkey
• iloveyou1
• superman1
• slipknot1
• jordan23
• princess1
• liverpool1
• monkey1
• baseball1
• 123abc
• qwerty1
• blink182
• myspace1
• pop
• user111
• 098765
• qweryuiopas
• qwe
• qwer
• qwert
• qwerty
• asdfg
• chort
• nah
• xak
• xakep
• 111111
• 12345
• 2013
• 2007
• 2207
• 110
• 5554
• 775
• 354
• 1982
• 123
• password
• 123456

Injects code

If successful at privilege escalation, Simda attempts to inject a DLL into the process space of winlogon.exe. This DLL is detected as PWS:Win32/Simda.

Exploits vulnerabilities

Backdoor:Win32/Simda.gen!A also attempts to exploit the following vulnerabilities in order to assist in gaining elevated privileges:

• MS10-092
• MS10-015
• CVE-2010-0232

Additional information

The retrieved domains are then saved to the following registry entries in an encrypted form, for example:

In subkey: HKLM\Software\Microsoft
Sets value: “m1131”
With data: <encrypted URL>


In subkey: HKLM\Software\Microsoft
Sets value: “m1132”
With data: <encrypted URL>


In subkey: HKLM\Software\Microsoft
Sets value: “m1133”
With data: <encrypted URL>

Analysis by Matt McCormack