Backdoor.Win32.BIFROSE.AE
Backdoor.Win32.Bifrose.yg (Kaspesky); Backdoor:Win32/Bifrose.gen!D [generic] (Microsoft); Backdoor.Bifrose.E (Norton)
Windows
Threat Type: Backdoor
Destructiveness: No
Encrypted: Yes
In the wild: Yes
OVERVIEW
This Backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.
It executes commands from a remote malicious user, effectively compromising the affected system.
TECHNICAL DETAILS
Arrival Details
This Backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.
Installation
This Backdoor drops the following copies of itself into the affected system:
- %System%\winrss.exe
(Note: %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)
It adds the following processes:
- {malware path}\{malware name} t
- %Program Files%\Internet Explorer\iexplore.exe
(Note: %Program Files% is the default Program Files folder, usually C:\Program Files in Windows 2000(32-bit), Server 2003(32-bit), XP, Vista(64-bit), 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit) , or C:\Program Files (x86) in Windows XP(64-bit), Vista(64-bit), 7(64-bit), 8(64-bit), 8.1(64-bit), 2008(64-bit), 2012(64-bit) and 10(64-bit).)
It adds the following mutexes to ensure that only one of its copies runs at any one time:
- 8D32
It injects itself into the following processes as part of its memory residency routine:
- %Windows%\explorer.exe
- %Program Files%\Internet Explorer\iexplore.exe
(Note: %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.. %Program Files% is the default Program Files folder, usually C:\Program Files in Windows 2000(32-bit), Server 2003(32-bit), XP, Vista(64-bit), 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit) , or C:\Program Files (x86) in Windows XP(64-bit), Vista(64-bit), 7(64-bit), 8(64-bit), 8.1(64-bit), 2008(64-bit), 2012(64-bit) and 10(64-bit).)
Autostart Technique
This Backdoor adds the following registry entries to enable its automatic execution at every system startup:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Active Setup\Installed Components\(CLSID)
stubpath = "%System%\winrss.exe s"
Other System Modifications
This Backdoor adds the following registry entries:
HKEY_LOCAL_MACHINE\Software\SKavx
nck = {encrypted "work@seup"}
HKEY_CURRENT_USER\Software\SKavx
klg = {hex value}
Backdoor Routine
This Backdoor executes the following commands from a remote malicious user:
- Capture screenshot
- Get device display resolution
- Send mouse input
- Close window
- Terminate process
- Get all running processes except for AV related processes named "kav.exe" and "kavsvc.exe"
- Get filenames of running processes
- Send keyboard input
- Set Window Text
- Send Window to Foreground
- Hide Window
- Execute Command / Open file Using ShellExecute
- Find File
- Rename File
- Delete Directory
- Delete File
- Create Directory
- Create File
- Get Drives' Type
- Get file/folder details (name, size)
- Execute a command line
- Enumerate Window Names
It connects to the following URL(s) to send and receive commands from a remote malicious user:
- webrss.{BLOCKED}6.org .
- usnews.{BLOCKED}bs.org
Other Details
This Backdoor adds the following registry keys:
HKEY_LOCAL_MACHINE\Software
SKavx =
HKEY_CURRENT_USER\Software
SKavx =
SOLUTION
Step 1
Trend Micro Predictive Machine Learning detects and blocks malware at the first sign of its existence, before it executes on your system. When enabled, your Trend Micro product detects this malware under the following machine learning name:
- Troj.Win32.TRX.XXPE50FFF036
Step 2
Before doing any scans, Windows 7, Windows 8, Windows 8.1, and Windows 10 users must disable System Restore to allow full scanning of their computers.
Step 3
Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.
Step 4
Restart in Safe Mode
Step 5
Delete this registry value
Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Active Setup\Installed Components\(CLSID)
- stubpath = "%System%\winrss.exe s"
- stubpath = "%System%\winrss.exe s"
- In HKEY_LOCAL_MACHINE\Software\SKavx
- nck = {encrypted work@seup}
- nck = {encrypted work@seup}
- In HKEY_CURRENT_USER\Software\SKavx
- klg = {hex value}
- klg = {hex value}
Step 6
Delete this registry key
Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.
- HKEY_LOCAL_MACHINE\Software\SKavx
- HKEY_CURRENT_USER\Software\SKavx
Step 7
Search and delete these files
- %System%\winrss.exe
Step 8
Restart in normal mode and scan your computer with your Trend Micro product for files detected as Backdoor.Win32.BIFROSE.AE. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check this Knowledge Base page for more information.
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