BKDR_ZACCESS

This description is based is a compiled analysis of several variants of BKDR_ZACCESS. Note that specific data such as file names and registry values may vary for each variant.

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 arrives as a component bundled with malware/grayware packages.

It connects to a website to send and receive information.

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

It may be used by other malware in performing their malicious routines. However, as of this writing, the said sites are inaccessible.

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 arrives as a component bundled with malware/grayware packages.

Installation

This backdoor drops the following files:

• %Windows%\{random numbers}
• %Application Data%\{random}\@
• %Application Data%\{random}\X

(Note: %Windows% is the Windows folder, which is usually C:\Windows or C:\WINNT.. %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}

(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 injects codes into the following process(es):

• explorer.exe

Autostart Technique

This backdoor 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}\X"

It registers as a system service to ensure its automatic execution at every system startup by adding the following registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{random}

Backdoor Routine

This backdoor connects to the following websites to send and receive information:

• {BLOCKED}212.157
• {BLOCKED}er.yadro.ru

Rootkit Capabilities

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

Other Details

This backdoor connects to the following possibly malicious URL:

• http://{BLOCKED}ur.cn/{BLOCKED}t2.php?w=15&i={random characters}&a=1
• http://{BLOCKED}ur.cn/{BLOCKED}d.php?w=15&fail=1&i={random characters}
• http://{BLOCKED}ur.cn/{BLOCKED}at2.php?w=15&i={random characters}&a=21
• http://{BLOCKED}ur.cn/{BLOCKED}t2.php?w=15&i={random characters}&a=20
• http://{BLOCKED}hu.cn/stat2.php?w={value}&i={value}&a={value}
• http://{BLOCKED}hu.cn/bad.php?w={value}&fail={value}&i={value}

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

NOTES:

It is capable of terminating security software and forensic tools that it finds accessing its components. It may also reset the access control list (ACL) setting of the terminated process's file, thus, effectively preventing it from executing again.

It is capable of overwriting a legitimate driver in the system as part of its installation and to execute itself during system startup.

This description is based is a compiled analysis of several variants of BKDR_ZACCESS. Note that specific data such as file names and registry values may vary for each variant.