BKDR_CRIDEX.QOR

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 is injected into all running processes to remain memory resident.

It executes commands from a remote malicious user, effectively compromising the affected system. It connects to a website to send and receive information.

It deletes itself after execution.

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 and executes them:

• %Application Data%\KB{random digit}.exe

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Roaming on Windows Vista and 7.)

It creates the following folders:

• %Application Data%\BF9BD00E

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Roaming on Windows Vista and 7.)

It is injected into all running processes to remain memory resident.

It adds the following mutexes to ensure that only one of its copies runs at any one time:

• Local\XMM{8 random characters}
• Local\XME{8 random characters}
• Local\XMI{8 random characters}
• Local\XMS{8 random characters}
• Local\XMF{8 random characters}
• Local\XMR{8 random characters}
• Local\XMQ{8 random characters}
• Local\XMB{8 random characters}

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
KB{random digit}.exe = "%Application Data%\KB{random digit}.exe"

Other System Modifications

This backdoor adds the following registry keys:

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\CD184B802

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\SBF9BD00E

It adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Internet Settings
GlobalUserOffline = "0"

Backdoor Routine

This backdoor executes the following commands from a remote malicious user:

• Monitor browser cookies
• Download and execute arbitrary files
• Upload stolen information
• Download configuration files

It connects to the following websites to send and receive information:

• http://{BLOCKED}rco.ru/{random}
• http://{BLOCKED}ltd.ru/{random}
• http://{BLOCKED}sdnl.ru/{random}
• http://{BLOCKED}wnloads17.ru/{random}

Other Details

This backdoor deletes itself after execution.

NOTES:

When this malware successfully connects to its C&C server, it can download configuration files wherein it is saved in the following registries:

HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CD184B802

HKEY_CURRENT_USER\Software\Microsoft\Windows NT\SBF9BD00E

The configuration file may contain information which is used to monitor browser activities, specifically the address bar or title, of the affected system. However, as of this writing, the mentioned sites above were already inaccessible.