BKDR_SERKDES.A


 ALIASES:

PWS:Win32/Serkdes.A (Microsoft)

 PLATFORM:

Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Downloaded from the Internet, Dropped by other malware

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 does not have any propagation routine.

It executes commands from a remote malicious user, effectively compromising the affected system. However, as of this writing, the said sites are inaccessible.

It deletes the initially executed copy of itself.

  TECHNICAL DETAILS

File Size:

Varies

File Type:

EXE, DLL

Memory Resident:

Yes

Initial Samples Received Date:

07 Jun 2013

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:

  • %User Temp%/Del{random number}.tmp
  • %System%\rasaut.dll

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Local\Temp on Windows Vista and 7.. %System% is the Windows system folder, which is usually C:\Windows\System32.)

Autostart Technique

This backdoor modifies the following registry entries to ensure it automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\ResAuto\Parameters
ServiceDll = "%System%\rasaut.dll"

(Note: The default value data of the said registry entry is %System%\rasauto.dll.)

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\RasAuto
Start = "2"

(Note: The default value data of the said registry entry is 3.)

Other System Modifications

This backdoor modifies the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\RasAuto
DisplayName = "Remote Access Auto Connection Manager" (Windows Vista and higher versions)

(Note: The default value data of the said registry entry is @%Systemroot%\system32\rasauto.dll,-200.)

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
services\RasAuto
Type = "288"

(Note: The default value data of the said registry entry is 32.)

Propagation

This backdoor does not have any propagation routine.

Backdoor Routine

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

  • Download file
  • Execute file
  • Delay process
  • Send system information such as host name and IP

It connects to the following URL(s) to send and receive commands from a remote malicious user:

  • paqsr.{BLOCKED}s.de:443
  • {BLOCKED}.2.9:443

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

Other Details

This backdoor deletes the initially executed copy of itself

NOTES:

It does not have rootkit capabilities.

It does not exploit any vulnerability.

  SOLUTION

Minimum Scan Engine:

9.300

FIRST VSAPI PATTERN FILE:

9.972.06

FIRST VSAPI PATTERN DATE:

10 Jun 2013

VSAPI OPR PATTERN File:

9.973.00

VSAPI OPR PATTERN Date:

11 Jun 2013

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

Scan your computer with your Trend Micro product and note files detected as BKDR_SERKDES.A

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

Restore this modified 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_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ResAuto\Parameters
    • From: ServiceDll = "%System%\rasaut.dll"
      To: ServiceDll = "%System%\rasauto.dll"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\RasAuto
    • From: Start = "2"
      To: Start = "3"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\RasAuto
    • From: DisplayName = "Remote Access Auto Connection Manager" (Windows Vista and higher versions)
      To: DisplayName = "@%Systemroot%\system32\rasauto.dll,-200"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\RasAuto
    • From: Type = "288"
      To: Type = "32"

Step 5

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