BKDR_ZACCESS.YM
TrojanDropper:Win32/Sirefef.gen!E(Microsoft), Trojan.Zeroaccess.C(Norton), ZeroAccess(McAfee), Backdoor.Win32.ZAccess(Ikarus), Win32/Sirefef.FU trojan(Eset)
Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)
![](/vinfo/imgFiles/legend.jpg)
Threat Type: Backdoor
Destructiveness: No
Encrypted:
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 may be downloaded by other malware/grayware from remote sites.
It executes commands from a remote malicious user, effectively compromising the affected system.
It deletes itself after execution.
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.
It may be downloaded by the following malware/grayware from remote sites:
- TSPY_FAREIT.TO
Installation
This backdoor drops the following file(s)/component(s):
- %System Root%\RECYCLER\S-1-5-18\${random}\@ - Detected as Mal_Xin12
- %System Root%\RECYCLER\S-1-5-18\${random}\n - Detected as TROJ_SIREFEF.AFP
- %System Root%\RECYCLER\S-1-5-21-{random}\$I{random} - Contains stolen information
- %System Root%\RECYCLER\S-1-5-21-{random}\$R{random} - Contains stolen information
- %System Root%\RECYCLER\S-1-5-21-{random}\${random}\@ - Detected as Mal_Xin12
- %System Root%\RECYCLER\S-1-5-21-{random}\${random}\n - Detected as TROJ_SIREFEF.AFP
(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)
It creates the following folders:
- %System Root%\RECYCLER\S-1-5-18\${random}
- %System Root%\RECYCLER\S-1-5-21-{random}
- %System Root%\RECYCLER\S-1-5-21-{random}\${random}
(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)
It injects threads into the following normal process(es):
- services.exe
Other System Modifications
This backdoor adds the following registry keys:
HKEY_CURRENT_USER\Software\Classes\
CLSID\{random}
HKEY_CURRENT_USER\Software\Classes\
CLSID\{random}\InprocServer32
It adds the following registry entries:
HKEY_CURRENT_USER\Software\Classes\
CLSID\{random}\InprocServer32
ThreadingModel = "Both"
HKEY_CURRENT_USER\Software\Classes\
CLSID\{random}\InprocServer32
(Default) = "%System Root%\RECYCLER\S-1-5-21-{random}\$BD{random}\n."
It modifies the following registry entries:
HKEY_CLASSES_ROOT\CLSID\{random}\
InprocServer32
(Default) = "%System Root%\RECYCLER\S-1-5-18\$BD{random}\n."
(Note: The default value data of the said registry entry is %System%\wbem\fastprox.dll.)
HKEY_CLASSES_ROOT\CLSID\{random}\
InProcServer32
(Default) = "%System Root%\RECYCLER\S-1-5-21-{random}\$BD{random}\n"
(Note: The default value data of the said registry entry is %System%\SHELL32.dll.)
HKEY_CLASSES_ROOT\CLSID\{random}\
InProcServer32
ThreadingModel = "Both"
(Note: The default value data of the said registry entry is Apartment.)
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
CLSID\{random}\InprocServer32
(Default) = "%System Root%\RECYCLER\S-1-5-18\$BD{random}\n."
(Note: The default value data of the said registry entry is %System%\wbem\fastprox.dll.)
It deletes the following registry keys:
HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Run\
Windows Defender
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_SHAREDACCESS
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_WSCSVC
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\wscsvc
Backdoor Routine
This backdoor executes the following commands from a remote malicious user:
- Get drive information
- Download arbitrary files
- Execute files
It connects to the following URL(s) to send and receive commands from a remote malicious user:
- {BLOCKED}.{BLOCKED}.215.6
- http://{BLOCKED}terbeaclesaapgcbzecj.com/ZmfaT1RVMmmgdj0xLjImaWQ9MTE5MzM1OTYyNiZhaWQ9MzA1MzQmc2lkPTAmb3M9NS4xLTMywvmueI4V
Process Termination
This backdoor terminates the following processes if found running in the affected system's memory:
- MSASCui.exe
- MpCmdRun.exe
- MisSrv.exe
- msseces.exe
- wsctfy.exe
- MsMpSvc
- windefend
- SharedAccess
- iphlpsvc
- wscsvc
- mpssvc
- bfe
Other Details
This backdoor deletes itself after execution.
It accesses the following URL(s) to get the affected system's location:
- http:// j.maxmind.com/app/geoip.js
NOTES:
This malware deletes registries related to Firewall restrictions.
SOLUTION
Step 1
Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.
Step 2
Remove the malware/grayware file that dropped/downloaded BKDR_ZACCESS.YM
- TSPY_FAREIT.TO
Step 3
Restart in Safe Mode
Step 4
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.
- In HKEY_CURRENT_USER\Software\Classes\CLSID
- {random}
- {random}
Step 5
Restore this modified 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_CLASSES_ROOT\CLSID\{random}\InprocServer32
- From: (Default) = "%System Root%\RECYCLER\S-1-5-18\$BD{random}\n."
To: (Default) = %System%\wbem\fastprox.dll
- From: (Default) = "%System Root%\RECYCLER\S-1-5-18\$BD{random}\n."
- In HKEY_CLASSES_ROOT\CLSID\{random}\InProcServer32
- From: (Default) = "%System Root%\RECYCLER\S-1-5-21-{random}\$BD{random}\n"
To: (Default) = %System%\SHELL32.dll
- From: (Default) = "%System Root%\RECYCLER\S-1-5-21-{random}\$BD{random}\n"
- In HKEY_CLASSES_ROOT\CLSID\{random}\InProcServer32
- From: ThreadingModel = "Both"
To: ThreadingModel = Apartment
- From: ThreadingModel = "Both"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{random}\InprocServer32
- From: (Default) = "%System Root%\RECYCLER\S-1-5-18\$BD{random}\n."
To: (Default) = %System%\wbem\fastprox.dll
- From: (Default) = "%System Root%\RECYCLER\S-1-5-18\$BD{random}\n."
Step 6
Restore these deleted registry keys/values from backup
*Note: Only Microsoft-related keys/values will be restored. If the malware/grayware also deleted registry keys/values related to programs that are not from Microsoft, please reinstall those programs on your computer.
- HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_SHAREDACCESS
- HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_WSCSVC
- HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess
- HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\wscsvc
- HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run\Windows Defender
Step 7
Search and delete these folders
- %System Root%\RECYCLER\S-1-5-18\${random}
- %System Root%\RECYCLER\S-1-5-21-{random}
Step 8
Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_ZACCESS.YM. 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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