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Added to the Dr.Web virus database: 2021-11-03

Virus description added:

Packer: UPX

  • SHA1 hash: be4d8344669f73e9620b9060fd87bc519a05617a


A backdoor written in Go and packed via UPX. Investigated backdoor version V2.5.5 z 2021.7.19.

Operating routine

At the beginning of the work, the malicious code checks whether another copy of the backdoor is running. The trojan checks for the [string]c:\windows\inf\mdmslbv.inf[/string] file and, if it exists, starts reading. You can use the following script to decrypt:

import sys
with open(sys.argv[1], 'rb') as f:
    d =
s = bytearray()
for i in range(len(d)):
for i in range(len(s)-2, 0, -1):
    s[i] = (((s[i + 1] * s[i + 1]) ^ s[i]) & 0xff)
with open(sys.argv[1] + '.dec', 'wb') as f:

Encrypted file’s length


The packet’s structure:

  • random string from 10 to 19 characters long;
  • between the <a>...</a> tags contains the PID of the backdoor process;
  • between the <b>...</b> tags is the name of the process;
  • random string from 10 to 19 characters long.

The trojan checks for the existence of a process with the specified parameters and, if it finds it, terminates its work.

If a process with the specified parameters or the [string]mdmslbv.inf[/string] file itself was not found, the Trojan generates data as shown above, encrypts and writes to the [string]c:\windows\inf\mdmslbv.inf[/ string].

Communication with the command and control server

The trojan has command and control server: [string] blog[.]globnewsline[.]com [/[/string]]

The trojan sends a GET request to the following URL: [string] hxxps:// [/string] using User-Agent "Mozilla/5.0 (X11; Windows x86_64; rv:70.0) Gecko/20100101 Firefox/70.0". If the server response contains the substring [string] Website under construction [/string], then the trojan considers that the control server is available. If the server is unavailable, the malicious code checks for the presence of a proxy configuration file [string] c:\windows\inf\bksotw.inf [/string] and, if present, reads the parameters written in the file.

The backdoor uses MAC addresses as the network interface bot ID. For heartbeat requests, the following POST requests are used:<macaddr>.t

where [string] <macaddr> [/string] is the MAC address string, converted to uppercase with colons removed.

Next, a GET request is sent to get a list of commands:<macaddr>.c

The server response is encrypted in the same way as the file with the PID of the backdoor process.

The following commands can be executed:

  • up;
  • down;
  • bg;
  • bgd;
  • getinfo.

The result of the command is encrypted in the same way as the command was encrypted, and sent in the body of the POST request to the following URL:<macaddr>.c

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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Download by serial number

  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