Analysis by: Rika Joi Gregorio
ALIASES:

Trojan:Win32/Sirefef.P(Microsoft), Trojan-Ransom.Win32.PornoAsset.bpwi(Kaspersky), a variant of Win32/Kryptik.ASKU trojan(Eset), Mal/ZAccess-AR(Sophos)

 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:

  • In the wild: Yes

  OVERVIEW

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.

  TECHNICAL DETAILS

File Size: 178,688 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 19 Jan 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 files:

  • %System Root%\RECYCLER\S-1-5-18\${random}\@
  • %System Root%\RECYCLER\S-1-5-18\${random}\N
  • %System Root%\RECYCLER\SS-1-5-21-527237240-651377827-1801674531-1003\${random}\@
  • %System Root%\RECYCLER\S-1-5-21-527237240-651377827-1801674531-1003\${random}\N

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

Autostart Technique

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

HKEY_CURRENT_USER\Software\Classes\
CLSID\{fbeb8a05-beee-4442-804e-409d6c4515e9}\InprocServer32
{Default} = "%System Root%\RECYCLER\S-1-5-21-527237240-651377827-1801674531-1003\${random}\n."

It modifies the following registry entry(ies) to enable its automatic execution at every system startup:

HKEY_CLASSES_ROOT\CLSID\{5839FCA9-774D-42A1-ACDA-D6A79037F57F}\
InprocServer32
{Default} = "%System Root%\RECYCLER\S-1-5-18\${random}\n."

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

Other System Modifications

This backdoor adds the following registry keys:

HKEY_CURRENT_USER\Software\Classes\
CLSID\{fbeb8a05-beee-4442-804e-409d6c4515e9}

HKEY_CURRENT_USER\Software\Classes\
CLSID\{fbeb8a05-beee-4442-804e-409d6c4515e9}\InprocServer32

HKEY_USERS\.DEFAULT\Software\
Microsoft\Internet Explorer\Main\
featurecontrol

HKEY_USERS\.DEFAULT\Software\
Microsoft\Internet Explorer\Main\
featurecontrol\FEATURE_BROWSER_EMULATION

It adds the following registry entries:

HKEY_CURRENT_USER\Software\Classes\
CLSID\{fbeb8a05-beee-4442-804e-409d6c4515e9}\InprocServer32
ThreadingModel = "Both"

HKEY_USERS\.DEFAULT\Software\
Microsoft\Internet Explorer\Main\
featurecontrol\FEATURE_BROWSER_EMULATION
svchost.exe = 8000

It modifies the following registry entries:

HKEY_CLASSES_ROOT\CLSID\{fbeb8a05-beee-4442-804e-409d6c4515e9}\
InProcServer32
ThreadingModel = "Both"

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

HKEY_CLASSES_ROOT\CLSID\{fbeb8a05-beee-4442-804e-409d6c4515e9}\
InProcServer32
{Default} = "%System Root%\RECYCLER\S-1-5-21-527237240-651377827-1801674531-1003\${random}\n."

(Note: The default value data of the said registry entry is %System%\SHELL32.dll.)

It deletes the following registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_BITS

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_SHAREDACCESS

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_WSCSVC

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_WUAUSERV

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\BITS

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\wuauserv

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\wscsvc

Other Details

This backdoor connects to the following possibly malicious URL:

  • http://j.{BLOCKED}d.com

  SOLUTION

Minimum Scan Engine: 9.300
FIRST VSAPI PATTERN FILE: 9.710.01
FIRST VSAPI PATTERN DATE: 06 Feb 2013
VSAPI OPR PATTERN File: 9.711.00
VSAPI OPR PATTERN Date: 07 Feb 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

Restart in Safe Mode

[ Learn More ]

Step 3

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.

 
  • HKEY_CURRENT_USER\Software\Classes\CLSID\{fbeb8a05-beee-4442-804e-409d6c4515e9}
  • HKEY_USERS\.DEFAULT\Software\Microsoft\Internet Explorer\Main\featurecontrol

Step 4

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\Classes\CLSID\{fbeb8a05-beee-4442-804e-409d6c4515e9}\InprocServer32
    • {Default} = "%System Root%\RECYCLER\S-1-5-21-527237240-651377827-1801674531-1003\${random}\n."

Step 5

Restore these modified registry values

[ Learn More ]

Important:Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this only if you know how to or you can seek your system administrator's help. You may also check out this Microsoft article first before modifying your computer's registry.

  • In HKEY_CLASSES_ROOT\CLSID\{5839FCA9-774D-42A1-ACDA-D6A79037F57F}\InprocServer32
    • From: Default = "%System Root%\RECYCLER\S-1-5-18\$082f346d1afdef957a415848b36bed23\n."
      To: Default = %System%\wbem\fastprox.dll
  • In HKEY_CLASSES_ROOT\CLSID\{fbeb8a05-beee-4442-804e-409d6c4515e9}\InProcServer32
    • From: {Default} = "%System Root%\RECYCLER\S-1-5-21-527237240-651377827-1801674531-1003\${random}\n."
      To: {Default} = %System%\SHELL32.dll
  • In HKEY_CLASSES_ROOT\CLSID\{fbeb8a05-beee-4442-804e-409d6c4515e9}\InProcServer32
    • From: ThreadingModel = "Both"
      To: ThreadingModel = Apartment

Step 6

Search and delete these folders

[ 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.
  • %System Root%\RECYCLER\S-1-5-21-527237240-651377827-1801674531-1003\${random}\@
  • %System Root%\RECYCLER\S-1-5-21-527237240-651377827-1801674531-1003\${random}\N
  • %System Root%\RECYCLER\S-1-5-18\${random}\@
  • %System Root%\RECYCLER\S-1-5-18\${random}\N

Step 7

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

Step 8

Restore these deleted registry keys/values from backup

*Note: Only Microsoft-related keys/values will be restored. If the malware/grayware also deleted registry keys/values related to programs that are not from Microsoft, please reinstall those programs on your computer.

  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_BITS
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_SHAREDACCESS
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_WSCSVC
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_WUAUSERV
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\BITS
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\wuauserv
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\wscsvc


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