TROJ_PASTA.PAFK
Trojan:Win32/Startpage.gen!A (Microsoft); StartPage-NX (McAfee); W32.SillyFDC (Symantec); Trojan.Win32.Pasta.kri (Kaspersky); Trojan.Win32.Pasta.kri (v) (Sunbelt); Trojan horse Startpage.IIG (AVG)
Windows 2000, Windows XP, Windows Server 2003
Threat Type: Trojan
Destructiveness: No
Encrypted:
In the wild: Yes
OVERVIEW
This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.
TECHNICAL DETAILS
Arrival Details
This Trojan 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 Trojan drops the following copies of itself into the affected system:
- %User Profile%\Application Data\cssrs.exe
(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.)
Autostart Technique
This Trojan adds the following registry entries to enable its automatic execution at every system startup:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
TINTIMG = "%User Profile%\Application Data\cssrs.exe"
Other System Modifications
This Trojan adds the following registry keys:
HKEY_CURRENT_USER\Software\Microsoft\
Internet Explorer\AboutURLs
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced\Folder\Hidden\
SHOWALL
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced\Folder\Hidden\
SuperHidden
HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced\Folder\Hidden\
SuperHidden
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced\Folder\HideFileExt
It adds the following registry entries:
HKEY_CURRENT_USER\Software\Microsoft\
Internet Explorer\Main
Default_Page_URL = "http://www.{BLOCKED}6.info"
HKEY_CURRENT_USER\Software\Microsoft\
Internet Explorer\AboutURLs
blank = "http://www.{BLOCKED}6.info"
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Internet Explorer\AboutURLs
Tabs = "http://www.{BLOCKED}6.info"
HKEY_CURRENT_USER\Software\Microsoft\
Internet Explorer\AboutURLs
Tabs = "http://www.{BLOCKED}6.info"
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
Hidden = "2"
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
ShowSuperHidden = "0"
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
HideFileExt = "1"
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced\Folder\Hidden\
SHOWALL
CheckedValue = "0"
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced\Folder\Hidden\
SuperHidden
CheckedValue = "1"
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced\Folder\Hidden\
SuperHidden
CheckedValue = "1"
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced\Folder\HideFileExt
CheckedValue = "1"
It modifies the following registry entries:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Internet Explorer\Main
Start Page = "http://www.{BLOCKED}6.info"
(Note: The default value data of the said registry entry is http://www.microsoft.com/isapi/redir.dll?prd={SUB_PRD}&clcid={SUB_CLSID}&pver={SUB_PVER}&ar=home.)
HKEY_CURRENT_USER\Software\Microsoft\
Internet Explorer\Main
Start Page = "http://www.{BLOCKED}6.info"
(Note: The default value data of the said registry entry is http://www.microsoft.com/isapi/redir.dll?prd=ie&pver=6&ar=msnhome.)
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Internet Explorer\Main
Default_Page_URL = "http://www.{BLOCKED}6.info"
(Note: The default value data of the said registry entry is http://www.microsoft.com/isapi/redir.dll?prd=ie&pver=6&ar=msnhome.)
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Internet Explorer\AboutURLs
blank = "http://www.{BLOCKED}6.info"
(Note: The default value data of the said registry entry is res://mshtml.dll/blank.htm.)
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
Hidden = "2"
(Note: The default value data of the said registry entry is 2.)
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced
HideFileExt = "1"
(Note: The default value data of the said registry entry is 1.)
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced\Folder\Hidden\
SHOWALL
CheckedValue = "0"
(Note: The default value data of the said registry entry is 1.)
Dropping Routine
This Trojan drops the following files:
- %User Startup%\cssrs.exe
(Note: %User Startup% is the current user's Startup folder, which is usually C:\Windows\Profiles\{user name}\Start Menu\Programs\Startup on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Start Menu\Programs\Startup on Windows NT, and C:\Documents and Settings\{User name}\Start Menu\Programs\Startup.)
This report is generated via an automated analysis system.
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
Restart in Safe Mode
Step 3
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\Microsoft\Internet Explorer
- AboutURLs
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Folder\Hidden
- SHOWALL
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Folder\Hidden
- SuperHidden
- In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Folder\Hidden
- SuperHidden
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Folder
- HideFileExt
Step 4
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\Windows\CurrentVersion\Run
- TINTIMG = "%User Profile%\Application Data\cssrs.exe"
- In HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main
- Default_Page_URL = "http://www.{BLOCKED}6.info"
- In HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\AboutURLs
- blank = "http://www.{BLOCKED}6.info"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\AboutURLs
- Tabs = "http://www.{BLOCKED}6.info"
- In HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\AboutURLs
- Tabs = "http://www.{BLOCKED}6.info"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Advanced
- Hidden = "2"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Advanced
- ShowSuperHidden = "0"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Advanced
- HideFileExt = "1"
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Folder\Hidden\SHOWALL
- CheckedValue = "0"
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Folder\Hidden\SuperHidden
- CheckedValue = "1"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Folder\Hidden\SuperHidden
- CheckedValue = "1"
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Folder\HideFileExt
- CheckedValue = "1"
Step 5
Restore these modified registry values
Important:Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this only if you know how to or you can seek your system administrator's help. You may also check out this Microsoft article first before modifying your computer's registry.
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\Main
- From: Start Page = "http://www.{BLOCKED}6.info"
To: Start Page = ""http://www.microsoft.com/isapi/redir.dll?prd={SUB_PRD}&clcid={SUB_CLSID}&pver={SUB_PVER}&ar=home""
- From: Start Page = "http://www.{BLOCKED}6.info"
- In HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main
- From: Start Page = "http://www.{BLOCKED}6.info"
To: Start Page = ""http://www.microsoft.com/isapi/redir.dll?prd=ie&pver=6&ar=msnhome""
- From: Start Page = "http://www.{BLOCKED}6.info"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\Main
- From: Default_Page_URL = "http://www.{BLOCKED}6.info"
To: Default_Page_URL = ""http://www.microsoft.com/isapi/redir.dll?prd=ie&pver=6&ar=msnhome""
- From: Default_Page_URL = "http://www.{BLOCKED}6.info"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\AboutURLs
- From: blank = "http://www.{BLOCKED}6.info"
To: blank = ""res://mshtml.dll/blank.htm""
- From: blank = "http://www.{BLOCKED}6.info"
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
- From: Hidden = "2"
To: Hidden = ""2""
- From: Hidden = "2"
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
- From: HideFileExt = "1"
To: HideFileExt = ""1""
- From: HideFileExt = "1"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Folder\Hidden\SHOWALL
- From: CheckedValue = "0"
To: CheckedValue = ""1""
- From: CheckedValue = "0"
Step 6
Search and delete this file
- %User Startup%\cssrs.exe
Step 7
Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_PASTA.PAFK. 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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