Backdoor:Win32/CoreFlood.B is a detection for a DLL component of
Win32/Afcore, a backdoor trojan that allows unauthorized remote access and control of an affected computer.
Installation
Backdoor:Win32/CoreFlood.B is installed by other malware. The trojan executes by being injected into a legitimate Windows process by its installer. When executed, the malware creates a randomized system event name based on file system and volume information, for example "\BaseNamedObjects\otypprkdephyksqufjlwam". It then creates a NULL mutex to assert that only one instance of the backdoor is running at a time.
Backdoor:Win32/CoreFlood.B drops the following files:
%windir%\system32\<random 1>.dll
%windir%\system32\<random 1>.dat
%windir%\system32\<random 2>.dat
%windir%\system32\<random 3>.dat
%windir%\system32\<random 3>.dat
Where <random> is a 6-7 character random file name, for example:
%windir%\system32\kbdfuht.dll - Backdoor:Win32/CoreFlood.B
%windir%\system32\kbdfuht.dat - data file
%windir%\system32\colbawt.dat - data file
%windir%\system32\msipx.dat - data file
%windir%\system32\onexmq.dat - data file
The registry is modified to run the malware component as in the following example:
In subkey: HKLM\Software\Classes\CLSID\{DB12B0FC-BB11-9114-DE28-165ADF40D7A3}
Sets value: "(default)"
With data: "kbdfuht"
In subkey: HKLM\SOFTWARE\Classes\CLSID\{DB12B0FC-BB11-9114-DE28-165ADF40D7A3}\InprocServer32
Sets value: "(default)"
With data: "<system folder>\kbdfuht.dll"
In subkey: HKLM\Software\Classes\CLSID\{DB12B0FC-BB11-9114-DE28-165ADF40D7A3}\InprocServer32
Sets value: "ThreadingModel"
With data: "Apartment"
In subkey: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\ShellIconOverlayIdentifiers\kbdfuht
Sets value: "(default)"
With data: "{DB12B0FC-BB11-9114-DE28-165ADF40D7A3}"
In subkey: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Browser Helper Objects\
Sets value: "(default)"
With data: "{DB12B0FC-BB11-9114-DE28-165ADF40D7A3}"
Note, the CLSID value above is different among samples of this malware. Backdoor:Win32/CoreFlood.B is injected into a system process such as 'Explorer.exe' to become active.
Payload
Communicates with a remote server
This trojan connects to a command and control (C&C) remote server to retrieve commands that are executed on the affected computer. The trojan may also function as a proxy and may download and execute other malware on the affected computer.
Allows unauthorized remote access and control
This trojan allows limited access and control from a remote attacker. It could perform one or more of following actions on an affected computer:
Execute arbitrary files
Restart or shutdown its currently running process
Start or uninstall the backdoor service
Delete cookies
Rename or delete a specified file
Hook or unhook APIs
Monitor window sockets
Connect to a remote host to transmit system information and other data
Analysis by Rex Plantado
Take the following steps to help prevent infection on your computer:
- Enable a firewall on your computer.
- Get the latest computer updates for all your installed software.
- Use up-to-date antivirus software.
- Limit user privileges on the computer.
- Use caution when opening attachments and accepting file transfers.
- Use caution when clicking on links to webpages.
- Avoid downloading pirated software.
- Protect yourself against social engineering attacks.
- Use strong passwords.
Enable a firewall on your computer
Use a third-party firewall product or turn on the Microsoft Windows Internet Connection Firewall.
Get the latest computer updates
Updates help protect your computer from viruses, worms, and other threats as they are discovered. It is important to install updates for all the software that is installed in your computer. These are usually available from vendor websites.
You can use the Automatic Updates feature in Windows to automatically download future Microsoft security updates while your computer is on and connected to the Internet.
Use up-to-date antivirus software
Limit user privileges on the computer
Starting with Windows Vista and Windows 7, Microsoft introduced User Account Control (UAC), which, when enabled, allowed users to run with least user privileges. This scenario limits the possibility of attacks by malware and other threats that require administrative privileges to run.
You can configure UAC in your computer to meet your preferences:
Use caution when opening attachments and accepting file transfers
Exercise caution with email and attachments received from unknown sources, or received unexpectedly from known sources. Use extreme caution when accepting file transfers from known or unknown sources.
Use caution when clicking on links to webpages
Exercise caution with links to webpages that you receive from unknown sources, especially if the links are to a webpage that you are not familiar with, unsure of the destination of, or suspicious of. Malicious software may be installed in your computer simply by visiting a webpage with harmful content.
Avoid downloading pirated software
Threats may also be bundled with software and files that are available for download on various torrent sites. Downloading "cracked" or "pirated" software from these sites carries not only the risk of being infected with malware, but is also illegal. For more information, see '
The risks of obtaining and using pirated software'.
Protect yourself from social engineering attacks
While attackers may attempt to exploit vulnerabilities in hardware or software to compromise a computer, they also attempt to exploit vulnerabilities in human behavior to do the same. When an attacker attempts to take advantage of human behavior to persuade the affected user to perform an action of the attacker's choice, it is known as 'social engineering'. Essentially, social engineering is an attack against the human interface of the targeted computer. For more information, see '
What is social engineering?'.
Use strong passwords
Attackers may try to gain access to your Windows account by guessing your password. It is therefore important that you use a strong password – one that cannot be easily guessed by an attacker. A strong password is one that has at least eight characters, and combines letters, numbers, and symbols. For more information, see
http://www.microsoft.com/protect/yourself/password/create.mspx.
