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RTKT_NECURS.PRE

May 19, 2014
 Analysis by: Adrian Cofreros
 ALIASES:

Trojan:WinNT/Necurs.A(Microsoft),Win32/TrojanDownloader.Necurs.A trojan(NOD32),Trojan horse Hider.YXR(AVG)

 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:
 INFORMATION EXPOSURE:

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Downloaded from the Internet, Dropped by other malware


This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites. It may be dropped by other malware.

It deletes the initially executed copy of itself.

  TECHNICAL DETAILS

File Size:

55,424 bytes

File Type:

SYS

Memory Resident:

Yes

Initial Samples Received Date:

07 May 2014

Payload:

Terminates processes, Hooks APIs

Arrival Details

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It may be dropped by the following malware:

Installation

This Trojan drops the following copies of itself into the affected system:

  • %System%\drivers\{random filename}.sys

(Note: %System% is the Windows system folder, which is usually C:\Windows\System32.)

Autostart Technique

This Trojan registers itself as a system service to ensure its automatic execution at every system startup by adding the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{malware filename}
NextInstance = "1"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{malware filename}\
0000
Service = "{malware filename}"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{malware filename}\
0000
Legacy = "1"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{malware filename}\
0000
ConfigFlags = "0"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{malware filename}\
0000
Class = "LegacyDriver"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{malware filename}\
0000
ClassGUID = "{GUID}"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{malware filename}\
0000
DeviceDesc = "{malware filename}"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{malware filename}\
0000\Control
*NewlyCreated* = "0"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{malware filename}\
0000\Control
ActiveService = "{malware filename}"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{random filename}
NextInstance = "1"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{random filename}\
0000
Service = "{random filename}"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{random filename}\
0000
Legacy = "1"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{random filename}\
0000
ConfigFlags = "0"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{random filename}\
0000
Class = "LegacyDriver"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{random filename}\
0000
ClassGUID = "{GUID}"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{random filename}\
0000
DeviceDesc = "{malware filename}"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{random filename}\
0000\Control
*NewlyCreated* = "0"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{random filename}\
0000\Control
ActiveService = "{malware filename}"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{random filename}
DisplayName = "{malware filename}.exe"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{random filename}
ImagePath = "%System%\drivers\{random filename}.sys"

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 filename}

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{malware filename}

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{malware filename}\
0000

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{malware filename}\
0000\Control

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{random filename}

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{random filename}\
0000

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{random filename}\
0000\Control

Rootkit Capabilities

This Trojan is used by other malware for its rootkit functionalities.

Other Details

This Trojan deletes the initially executed copy of itself

NOTES:

This Trojan disables services used by the following companies by modifying its code to return to unsuccessful status:

  • Agnitum Ltd
  • ALWIL Software
  • PC Tools
  • GRISOFT, s.r.o.
  • Avira GmbH
  • BITDEFENDER LLC
  • BitDefender SRL
  • Comodo Inc
  • Doctor Web Ltd
  • ESET, spol. s r.o.
  • FRISK Software International Ltd
  • Kaspersky Lab
  • Panda Software International
  • Check Point Software Technologies Ltd
  • BullGuard Ltd
  • antimalware
  • NovaShield Inc
  • CJSC Returnil Software
  • Anti-Virus
  • Sophos Plc
  • Comodo Security Solutions
  • Quick Heal Technologies
  • G DATA Software
  • Beijing Rising
  • Immunet Corporation
  • K7 Computing
  • Sunbelt Software
  • SUNBELT SOFTWARE
  • Beijing Jiangmin
  • VirusBuster Ltd
  • KProcessHacker

It disables drivers with the following names by modifying its code to return to unsuccessful status:

  • eeCtrl.sys
  • eraser.sys
  • SRTSP.sys
  • SRTSPIT.sys
  • SRTSP64.SYS
  • a2gffx86.sys
  • a2gffx64.sys
  • a2gffi64.sys
  • a2acc.sys
  • a2acc64.sys
  • mbam.sys
  • eamonm.sys
  • MaxProtector.sys
  • SDActMon.sys
  • tmevtmgr.sys
  • tmpreflt.sys
  • vcMFilter.sys
  • drivesentryfilterdriver2lite.sys
  • mpFilter.sys
  • PSINPROC.SYS
  • PSINFILE.SYS
  • amfsm.sys
  • amm8660.sys
  • amm6460.sys
  • caavFltr.sys
  • ino_fltr.sys
  • avmf.sys
  • PLGFltr.sys
  • AshAvScan.sys
  • csaav.sys
  • SegF.sys
  • eeyehv.sys
  • eeyehv64.sys
  • NovaShield.sys
  • BdFileSpy.sys
  • tkfsft.sys
  • tkfsft64.sys
  • tkfsavxp.sys
  • tkfsavxp64.sys
  • SMDrvNt.sys
  • ATamptNt.sys
  • V3Flt2k.sys
  • V3MifiNt.sys
  • V3Ift2k.sys
  • V3IftmNt.sys
  • ArfMonNt.sys
  • AhnRghLh.sys
  • AszFltNt.sys
  • OMFltLh.sys
  • V3Flu2k.sys
  • vcdriv.sys
  • vcreg.sys
  • vchle.sys
  • NxFsMon.sys
  • AntiLeakFilter.sys
  • NanoAVMF.sys
  • shldflt.sys
  • nprosec.sys
  • nregsec.sys
  • issregistry.sys
  • THFilter.sys
  • pervac.sys
  • avgmfx86.sys
  • avgmfx64.sys
  • avgmfi64.sys
  • avgmfrs.sys
  • fortimon2.sys
  • fortirmon.sys
  • fortishield.sys
  • savonaccess.sys
  • OADevice.sys
  • pwipf6.sys
  • EstRkmon.sys
  • EstRkr.sys
  • dwprot.sys
  • Spiderg3.sys
  • STKrnl64.sys
  • UFDFilter.sys
  • SCFltr.sys
  • fildds.sys
  • fsfilter.sys
  • fpav_rtp.sys
  • cwdriver.sys
  • Rtw.sys
  • HookSys.sys
  • snscore.sys
  • ssvhook.sys
  • strapvista.sys
  • strapvista64.sys
  • sascan.sys
  • savant.sys
  • vradfil2.sys
  • fsgk.sys
  • PCTCore64.sys
  • PCTCore.sys
  • ikfilesec.sys
  • ZxFsFilt.sys
  • antispyfilter.sys
  • PZDrvXP.sys
  • ggc.sys
  • catflt.sys
  • kmkuflt.sys
  • mfencoas.sys
  • mfehidk.sys
  • cmdguard.sys
  • K7Sentry.sys
  • nvcmflt.sys
  • issfltr.sys
  • AVCKF.SYS
  • bdfsfltr.sys
  • bdfm.sys
  • AVC3.SYS
  • aswmonflt.sys
  • HookCentre.sys
  • PktIcpt.sys
  • MiniIcpt.sys
  • avgntflt.sys
  • klbg.sys
  • kldback.sys
  • kldlinf.sys
  • kldtool.sys
  • klif.sys
  • lbd.sys
  • rvsmon.sys
  • ssfmonm.sys
  • KmxAgent.sys
  • KmxAMRT.sys
  • KmxAMVet.sys
  • KmxStart.sys
  • ahnflt2k.sys
  • AhnRec2k.sys
  • AntiyFW.sys
  • v3engine.sys
  • Vba32dNT.sys
  • kprocesshacker.sys

It hooks the following APIs:

  • NtOpenProcess
  • NtOpenThread

  SOLUTION

Minimum Scan Engine:

9.700

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

Remove the malware/grayware file that dropped/downloaded RTKT_NECURS.PRE

    • TSPY_ZBOT.PRE

Step 3

Scan your computer with your Trend Micro product and note files detected as RTKT_NECURS.PRE

Step 4

Restart in Safe Mode

[ Learn More ]

Step 5

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.

  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
    • {random filename}
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root
    • LEGACY_{malware filename}
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root
    • LEGACY_{random filename}

Step 6

Search and delete the file detected as RTKT_NECURS.PRE

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden files in the search result.

Step 7

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