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Trojan.Siggen6.31836

Added to the Dr.Web virus database: 2015-03-14

Virus description added:

This malware was designed to spread BackDoor.Yebot. Being written in Assembly, it targets Windows systems. When launched, the Trojan injects its code into svchost.exe, csrss.exe, lsass.exe and explorer.exe processes. Then, it sends the following request to the command and control server:

http://46.***.***.24/f/i.html?n=1&i=6C78E45B&s=22E2F&g=3&c=6C78E45B&pl=%5B
System%20Process%5D;0;0;System;4;0;smss.exe;368;4;csrss.exe;584;368;winlogon.exe;
608;368;services.exe;652;608;lsass.exe;664;608;VBoxService.exe;820;652;
svchost.exe;864;652;svchost.exe;952;652;svchost.exe;1044;652;svchost.exe;
1100;652;svchost.exe;1132;652;spoolsv.exe;1388;652;mscorsvw.exe;1516;652;
wuauclt.exe;1700;1044;alg.exe;2016;652;wmiprvse.exe;256;864;explorer.exe;
996;884;wscntfy.exe;1076;1044;VBoxTray.exe;1172;996;python.exe;1556;820;
18dacf3896cee9d20b15dfa6d912394e363252b9904798215edc4e4798c3e459;492;1556&r=
0.51103000.2600.1

The malware downloads BackDoor.Yebot from the remote server, decrypts it using an RC4 algorithm with the key c=6C78E45B, then performs all the manipulations in its memory and transfers control to the entry point of a dynamic link library.

Some of Trojan's features are encrypted and can be decrypted only while being executed. To perform this action a malicious program reserves the memory that is automatically freed when the feature's code is executed. Encrypting process implements the bytes' reordering, so that the entropy of the encrypted code does not change.

First, the Trojan sets the AddVectoredExceptionHandler parameter to intercept all exceptions, especially, "IN" privileged instructions. In this case, to provide anti-debugging in the Trojan's assembler code, some call instructions were replaced with "IN" instructions followed by one or two bytes. Examples of Trojan's code:

.text:00485A01                 push    18h
.text:00485A03                 push    0
.text:00485A05                 push    10h
.text:00485A07                 push    offset ExceptionHandler
.text:00485A0C                 push    offset TimerHandler
.text:00485A11                 push    offset unk_481934
.text:00485A16                 push    dword_481930
.text:00485A1C                 call    eax             ; ntdll_RtlCreateTimer
.text:00485A1E                 push    54Eh
.text:00485A23                 call    ds:Sleep
.text:00485A23 ; ---------------------------------------------------------------------------
.text:00485A29 Function_In_485a29 db 0ECh ; ь          ; 0x48417c GetAllAPIs
.text:00485A2A                 db  7Ch ; |
.text:00485A2B                 db  21h ; !
.text:00485A2C ; ---------------------------------------------------------------------------
.text:00485A2C                 push    1
.text:00485A2E                 push    offset unk_401730
.text:00485A2E ; ---------------------------------------------------------------------------
.text:00485A33                 db 0E4h ; ф     ; 0x4016d4 advapi32_InitializeSecurityDescriptor
.text:00485A34                 db  61h ; a
.text:00485A35 ; ---------------------------------------------------------------------------
.text:00485A35                 push    0
.text:00485A37                 push    0
.text:00485A39                 push    1
.text:00485A3B                 push    offset unk_401730
.text:00485A3B ; ---------------------------------------------------------------------------
.text:00485A40                 db 0E4h ; ф     ; 0x4016d8 advapi32_SetSecurityDescriptorDacl
.text:00485A41                 db  62h ; b
.text:00485A42 ; ---------------------------------------------------------------------------
.text:00485A42                 lea     edx, unk_401730

This malware also incorporates mechanisms to verify the virtual machine in a target system using the following algorithm:

  1. Monitoring of the SYSTEM\ControlSet001\Control\DeviceClasses registry branch for Ven_VMware_ line
  2. Checking an application SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall SysAnalyzer in the list of installed programs

The address of the command and control server is also encrypted by using an RC4 algorithm, the encryption code is in one of the encrypted features.

The Trojan incorporates a mechanism to bypass User Accounts Control using the Elevation: Administrator! new: {3ad05575-8857-4850-9277-11b85bdb8e09} vulnerability.

Curing recommendations

  1. If the operating system (OS) can be loaded (either normally or in safe mode), download Dr.Web Security Space and run a full scan of your computer and removable media you use. More about Dr.Web Security Space.
  2. If you cannot boot the OS, change the BIOS settings to boot your system from a CD or USB drive. Download the image of the emergency system repair disk Dr.Web® LiveDisk , mount it on a USB drive or burn it to a CD/DVD. After booting up with this media, run a full scan and cure all the detected threats.
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Use Dr.Web Anti-virus for macOS to run a full scan of your Mac.

After booting up, run a full scan of all disk partitions with Dr.Web Anti-virus for Linux.

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  1. If the mobile device is operating normally, download and install Dr.Web for Android. Run a full system scan and follow recommendations to neutralize the detected threats.
  2. If the mobile device has been locked by Android.Locker ransomware (the message on the screen tells you that you have broken some law or demands a set ransom amount; or you will see some other announcement that prevents you from using the handheld normally), do the following:
    • Load your smartphone or tablet in the safe mode (depending on the operating system version and specifications of the particular mobile device involved, this procedure can be performed in various ways; seek clarification from the user guide that was shipped with the device, or contact its manufacturer);
    • Once you have activated safe mode, install the Dr.Web for Android onto the infected handheld and run a full scan of the system; follow the steps recommended for neutralizing the threats that have been detected;
    • Switch off your device and turn it on as normal.

Find out more about Dr.Web for Android

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