RTKT_ZACCESS.E

 Analysis by: Sabrina Lei Sioting

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • 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.

It executes then deletes itself afterward.

It also has rootkit capabilities, which enables it to hide its processes and files from the user.

However, as of this writing, the said sites are inaccessible.

  TECHNICAL DETAILS

File Size:

250,880 bytes

Memory Resident:

Yes

Initial Samples Received Date:

28 Oct 2011

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 non-malicious file:

  • %Application Data%\{random foldername}\@

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Windows\Profiles\{user name}\Application Data on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Application Data on Windows NT, and C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, XP, and Server 2003.)

It creates the following folders:

  • %Application Data%\{random foldername}
  • %Application Data%\{random foldername}\U

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Windows\Profiles\{user name}\Application Data on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Application Data on Windows NT, and C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, XP, and Server 2003.)

It executes then deletes itself afterward.

Autostart Technique

This Trojan registers itself as a system service to ensure its automatic execution at every system startup by adding the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{random foldername}
ImagePath = "%Windows%\{random}:{random filename}.exe"

It adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\CurrentVersion\Winlogon
Shell = "%Application Data%\{random foldername}\X"

Other System Modifications

This Trojan adds the following registry keys:

HKEY_CLASSES_ROOT\Interface\{sid}

HKEY_CURRENT_USER\Software\{random folder name}

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{random folder name}

It creates the following registry entry(ies) to bypass Windows Firewall:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\DomainProfile\AuthorizedApplications\
List
%Windows%\explorer.exe = "%Windows%\explorer.exe:*:Enabled:Windows Explorer"

Rootkit Capabilities

This Trojan also has rootkit capabilities, which enables it to hide its processes and files from the user.

Dropping Routine

This Trojan drops the following files:

  • %Application Data%\{random foldername}\X - detected as BKDR_ZACESS.SMAE
  • %Windows%\{random}:{random filename}.exe - detected as TROJ_FAKEAL.K

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Windows\Profiles\{user name}\Application Data on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Application Data on Windows NT, and C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, XP, and Server 2003.. %Windows% is the Windows folder, which is usually C:\Windows or C:\WINNT.)

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}hu.cn/{BLOCKED}ad.php?w={parameter}&fail={parameter}&i={parameter}
  • http://{BLOCKED}hu.cn/{BLOCKED}t2.php?w={parameter}&i={parameter}&a={parameter}
  • http://{BLOCKED}hu.cn/{BLOCKED}.exe

However, as of this writing, the said sites are inaccessible.

  SOLUTION

Minimum Scan Engine:

9.200

FIRST VSAPI PATTERN FILE:

8.540.03

FIRST VSAPI PATTERN DATE:

01 Nov 2011

Step 1

For Windows XP and Windows Server 2003 users, before doing any scans, please make sure you disable System Restore to allow full scanning of your computer.

Step 2

Remove malware files dropped/downloaded by RTKT_ZACCESS.E

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

Delete this registry key

[ Learn More ]

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
    • {random foldername}
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
    • {random foldername}

Step 5

Delete this registry value

[ Learn More ]

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\Windows NT\CurrentVersion\Winlogon
    • Shell = "%Application Data%\{random foldername}\X"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\DomainProfile\AuthorizedApplications\List
    • %Windows%\explorer.exe = "%Windows%\explorer.exe:*:Enabled:Windows Explorer"

Step 6

Search and delete this file

[ Learn More ]
There may be some component files that are hidden. Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden files and folders in the search result.
  • %Windows%\{random}

Step 7

Search and delete this folder

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.  
  • %Application Data%\{random folder name}

Step 8

Restart in normal mode and scan your computer with your Trend Micro product for files detected as RTKT_ZACCESS.E. 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.

NOTES:
The string {random folder name} indicates the folder where the dropped files are placed. To identify this folder, take note of the following location of files:

  • %Application Data%\{random foldername}\X
  • %Windows%\{random}:{random filename}.exe

The SID cannot be identified by user since there are no reference values in the created key.

The only way it can be identified is by comparing the present keys with a backup if the users have one. Note that the key,{Sid} need not to be deleted since it won't cause the user system any harm.


Did this description help? Tell us how we did.