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Backdoor:Win32/Remosh.A


Backdoor:Win32/Remosh.A is a trojan that sends Windows system configuration details to a remote server and also allows remote access and control of the affected computer.


What to do now

To detect and remove this threat and other malicious software that may be installed in your computer, run a full-system scan with an up-to-date antivirus product such as the following:
 
 
For more information on antivirus software, see http://www.microsoft.com/windows/antivirus-partners/.

Threat behavior

Backdoor:Win32/Remosh.A is a trojan that sends Windows system configuration details to a remote server and also allows remote access and control of the affected computer.
Installation
Backdoor:Win32/Remosh.A is installed by a dropper trojan such as Backdoor:Win32/Remosh.A.dr and is present as a DLL component located in the Windows system folder. The DLL runs as a service at Windows start. Below is an example of one observed registry modification made by the trojan dropper after installing Backdoor:Win32/Remosh.A to run as a service:
 
Sets value: "ServiceDll"
With data: "<system folder>\hpmdp093.dll"
In subkey: HKLM\SYSTEM\CurrentControlSet\Services\6to4\Parameters
 
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.
 
It contains the following variables in its code; note that the actual values of the variables may change depending on the malware sample:
 
MUTEXNAME = "NT1630"
SHELLCOMMAND = "shell"
SERVICENAME = "6to4"
SERVICE_DISPLAYNAME = "ASP.NET Services"
SERVICE_DESCRIPTION = ""
DISABLE_IPSEC = "1"
MASTER_HOST = "<string>.is-a-chef.com"
MASTER_PORT = "80"
 
The malware checks for a mutex named "MUTEXNAME" to verify that it isn't already running. If found, it exits immediately; if not, it creates the mutex.
 
If the value of "DISABLE_IPSEC" is non-zero, the trojan stops and disables the "PolicyAgent" service, which is the IPSec service.
 
Win32/Remosh registers itself to run as a service named "SERVICENAME", with a display name "SERVICE_DISPLAYNAME" and a description as "SERVICE_DESCRIPTION". The service is configured so it cannot be stopped, however it does respond to system shutdown requests.
Payload
Allows remote access and control
Every 30 seconds, the malware establishes a TCP connection to "MASTER_HOST" on port "MASTER_PORT" - all subsequent communication is encrypted. The trojan sends system information (computer name, processor information, OS version).
 
The trojan accepts commands from the server if the server reply starts with "SHELLCOMMAND"; commands include the following:
  • enumerate terminal services sessions to show who is logged into the machine
  • enumerate system drives, collecting drive letters, types, free space and volume name
  • enumerate files by path, allowing the server to browse the contents of the file system
  • launch an executable remotely
  • open a remote command shell which allows the server to execute commands
  • enumerate registry keys
  • send screenshots from the local system to the server to show what is happening on the system
  • uninstall itself
  • move, delete or copy a file
  • set file attributes on a file
  • receive a new file from the server.
Additional Information
Note that the file name used by this trojan may vary from sample to sample. This is because this trojan is created using a construction toolkit known as "Gh0st Rat". Therefore, certain aspects of the trojan are author-defined such as the following:
  • Mutex name
  • Service name
  • Service display name
  • Service description
  • IPSEC options
  • Command and control server domain name
  • Command and control communication port
 
Analysis by Aaron Putnam

Symptoms

There are no common symptoms associated with this threat. Alert notifications from installed antivirus software may be the only symptoms.

Prevention


Alert level: Severe
First detected by definition: 1.87.1686.0
Latest detected by definition: 1.87.1686.0 and higher
First detected on: Aug 11, 2010
This entry was first published on: Aug 11, 2010
This entry was updated on: Apr 17, 2011

This threat is also detected as:
  • TR/Spy.Gen (Avira)
  • Trojan.Win32.Agent.egli (Kaspersky)
  • TROJ_AGENTT.SML (Trend Micro)
  • NightDragon (McAfee)
  • Night Dragon (other)