BKDR_DEXTR.A

This malware was discovered to target point of sale (POS) systems used in establishments such as restaurants and hotels in order to steal credit card information from purchasing customers. Purchasing from the establishments with infected systems may result in users' financial information being stolen, and may find themselves billed with unauthorized expenses made by cybercriminals.

To get a one-glance comprehensive view of the behavior of this Backdoor, refer to the Threat Diagram shown below.

For the related story, you may read the blog post Infostealer Dexter Targets Checkout Systems

This backdoor is also known as BlackPOS.

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 runs certain commands that it receives remotely from a malicious user. Doing this puts the affected computer and information found on the computer at greater risk.

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:

• %Application Data%\{random}\{random}.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 adds the following processes:

• iexplore.exe

It creates the following folders:

• %Application Data%\{random}

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

• WindowsResilienceServiceMutex

It injects itself into the following processes as part of its memory residency routine:

• iexplore.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\CurrentVersion\Run
{GUID} = "%Application Data%\{random}\{random}.exe"

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

Other System Modifications

This backdoor adds the following registry entries as part of its installation routine:

HKEY_CURRENT_USER\Software\Resilience Software
Digit = "{GUID}"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
Associations
LowRiskFileTypes = ".exe;.bat;.reg;.vbs;"

It adds the following registry keys as part of its installation routine:

HKEY_CURRENT_USER\Software\Resilience Software

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
Associations

Backdoor Routine

This backdoor executes the following command(s) from a remote malicious user:

• Update (update copy)
• Checkin (set the delay it sends information)
• Scanin (set the delay it checks memory for information)
• Uninstall (uninstall itself)
• Download (download and execute a file)

Information Theft

This backdoor gathers the following data:

• {GUID}
• Username
• Hostname
• Operating System
• Processor type
• List of running processes
• Key to decrypt sent information

Stolen Information

This backdoor sends the gathered information via HTTP POST to the following URL:

• http://{BLOCKED}.com/portal1/gateway.php
• http://{BLOCKED}.17.126/test/gateway.php

NOTES:

This backdoor dumps the affected system's memory to check for sensitive information, such as payment details and/or credit card information stored in the aforementioned system.