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WORM_YAHOS.F

June 18, 2013
 ALIASES:

VirTool:Win32/Injector.gen!CA (Microsoft); W32.Yimfoca!gen4 (Symantec); IM-Worm.Win32.Yahos.gt (Kaspersky); Trojan.Win32.Generic.pak!cobra (Sunbelt); Trojan horse Generic20.BCVB (AVG)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW


This worm 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:

81,920 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

14 Jun 2013

Arrival Details

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

Autostart Technique

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
NVIDIA driver monitor = "%Windows%\nvsvc32.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
NVIDIA driver monitor = "%Windows%\nvsvc32.exe"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Terminal Server\
Install\Software\Microsoft\
Windows\CurrentVersion\Run
NVIDIA driver monitor = "%Windows%\nvsvc32.exe"

Other System Modifications

This worm deletes the following files:

  • %System Root%\ndl.dl
  • %System Root%\ntdl.dl
  • %Windows%\ndl.dl
  • %Windows%\ntdl.dl

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

It adds the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\AuthorizedApplications\
List
{malware path and file name} = "{malware path and file name}:*:enabled:nvidia driver monitor"

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\AuthorizedApplications\
List
{malware path and file name} = "%Windows%\nvsvc32.exe:*:Enabled:NVIDIA driver monitor"

It modifies the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
SystemCertificates\AuthRoot\Certificates\
2F173F7DE99667AFA57AF80AA2D1B12FAC830338
Blob = "{random values}"

(Note: The default value data of the said registry entry is {random values}.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
SystemCertificates\AuthRoot\Certificates\
4EFCED9C6BDD0C985CA3C7D253063C5BE6FC620C
Blob = "{random values}"

(Note: The default value data of the said registry entry is {random values}.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
SystemCertificates\AuthRoot\Certificates\
4EF2E6670AC9B5091FE06BE0E5483EAAD6BA32D9
Blob = "{random values}"

(Note: The default value data of the said registry entry is {random values}.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
SystemCertificates\AuthRoot\Certificates\
4C95A9902ABE0777CED18D6ACCC3372D2748381E
Blob = "{random values}"

(Note: The default value data of the said registry entry is {random values}.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
SystemCertificates\AuthRoot\Certificates\
4BA7B9DDD68788E12FF852E1A024204BF286A8F6
Blob = "{random values}"

(Note: The default value data of the said registry entry is {random values}.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
SystemCertificates\AuthRoot\Certificates\
4B421F7515F6AE8A6ECEF97F6982A400A4D9224E
Blob = "{random values}"

(Note: The default value data of the said registry entry is {random values}.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
SystemCertificates\AuthRoot\Certificates\
47AFB915CDA26D82467B97FA42914468726138DD
Blob = "{random values}"

(Note: The default value data of the said registry entry is {random values}.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
SystemCertificates\AuthRoot\Certificates\
4463C531D7CCC1006794612BB656D3BF8257846F
Blob = "{random values}"

(Note: The default value data of the said registry entry is {random values}.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
SystemCertificates\AuthRoot\Certificates\
43F9B110D5BAFD48225231B0D0082B372FEF9A54
Blob = "{random values}"

(Note: The default value data of the said registry entry is {random values}.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
SystemCertificates\AuthRoot\Certificates\
43DDB1FFF3B49B73831407F6BC8B975023D07C50
Blob = "{random values}"

(Note: The default value data of the said registry entry is {random values}.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
SystemCertificates\AuthRoot\Certificates\
40E78C1D523D1CD9954FAC1A1AB3BD3CBAA15BFC
Blob = "{random values}"

(Note: The default value data of the said registry entry is {random values}.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
SystemCertificates\AuthRoot\Certificates\
4072BA31FEC351438480F62E6CB95508461EAB2F
Blob = "{random values}"

(Note: The default value data of the said registry entry is {random values}.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
SystemCertificates\AuthRoot\Certificates\
3F85F2BB4A62B0B58BE1614ABB0D4631B4BEF8BA
Blob = "{random values}"

(Note: The default value data of the said registry entry is {random values}.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
SystemCertificates\AuthRoot\Certificates\
394FF6850B06BE52E51856CC10E180E882B385CC
Blob = "{random values}"

(Note: The default value data of the said registry entry is {random values}.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
SystemCertificates\AuthRoot\Certificates\
36863563FD5128C7BEA6F005CFE9B43668086CCE
Blob = "{random values}"

(Note: The default value data of the said registry entry is {random values}.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
SystemCertificates\AuthRoot\Certificates\
317A2AD07F2B335EF5A1C34E4B57E8B7D8F1FCA6
Blob = "{random values}"

(Note: The default value data of the said registry entry is {random values}.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
SystemCertificates\CA\Certificates\
E5215D3460C2C20BBE2D9FE5FB665DAA2C0E225C
Blob = "{random values}"

(Note: The default value data of the said registry entry is {random values}.)

Dropping Routine

This worm drops the following files:

  • %Windows%\nvsvc32.exe

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

Other Details

This worm connects to the following possibly malicious URL:

  • http://{BLOCKED}5.106.162/index.php

This report is generated via an automated analysis system.

  SOLUTION

Minimum Scan Engine:

9.300

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 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\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • NVIDIA driver monitor = "%Windows%\nvsvc32.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • NVIDIA driver monitor = "%Windows%\nvsvc32.exe"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Terminal Server\Install\Software\Microsoft\Windows\CurrentVersion\Run
    • NVIDIA driver monitor = "%Windows%\nvsvc32.exe"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\AuthorizedApplications\List
    • {malware path and file name} = "{malware path and file name}:*:enabled:nvidia driver monitor"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\AuthorizedApplications\List
    • {malware path and file name} = "%Windows%\nvsvc32.exe:*:Enabled:NVIDIA driver monitor"

Step 4

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_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates\AuthRoot\Certificates\2F173F7DE99667AFA57AF80AA2D1B12FAC830338
    • From: Blob = "{random values}"
      To: Blob = ""{random values}""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates\AuthRoot\Certificates\4EFCED9C6BDD0C985CA3C7D253063C5BE6FC620C
    • From: Blob = "{random values}"
      To: Blob = ""{random values}""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates\AuthRoot\Certificates\4EF2E6670AC9B5091FE06BE0E5483EAAD6BA32D9
    • From: Blob = "{random values}"
      To: Blob = ""{random values}""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates\AuthRoot\Certificates\4C95A9902ABE0777CED18D6ACCC3372D2748381E
    • From: Blob = "{random values}"
      To: Blob = ""{random values}""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates\AuthRoot\Certificates\4BA7B9DDD68788E12FF852E1A024204BF286A8F6
    • From: Blob = "{random values}"
      To: Blob = ""{random values}""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates\AuthRoot\Certificates\4B421F7515F6AE8A6ECEF97F6982A400A4D9224E
    • From: Blob = "{random values}"
      To: Blob = ""{random values}""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates\AuthRoot\Certificates\47AFB915CDA26D82467B97FA42914468726138DD
    • From: Blob = "{random values}"
      To: Blob = ""{random values}""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates\AuthRoot\Certificates\4463C531D7CCC1006794612BB656D3BF8257846F
    • From: Blob = "{random values}"
      To: Blob = ""{random values}""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates\AuthRoot\Certificates\43F9B110D5BAFD48225231B0D0082B372FEF9A54
    • From: Blob = "{random values}"
      To: Blob = ""{random values}""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates\AuthRoot\Certificates\43DDB1FFF3B49B73831407F6BC8B975023D07C50
    • From: Blob = "{random values}"
      To: Blob = ""{random values}""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates\AuthRoot\Certificates\40E78C1D523D1CD9954FAC1A1AB3BD3CBAA15BFC
    • From: Blob = "{random values}"
      To: Blob = ""{random values}""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates\AuthRoot\Certificates\4072BA31FEC351438480F62E6CB95508461EAB2F
    • From: Blob = "{random values}"
      To: Blob = ""{random values}""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates\AuthRoot\Certificates\3F85F2BB4A62B0B58BE1614ABB0D4631B4BEF8BA
    • From: Blob = "{random values}"
      To: Blob = ""{random values}""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates\AuthRoot\Certificates\394FF6850B06BE52E51856CC10E180E882B385CC
    • From: Blob = "{random values}"
      To: Blob = ""{random values}""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates\AuthRoot\Certificates\36863563FD5128C7BEA6F005CFE9B43668086CCE
    • From: Blob = "{random values}"
      To: Blob = ""{random values}""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates\AuthRoot\Certificates\317A2AD07F2B335EF5A1C34E4B57E8B7D8F1FCA6
    • From: Blob = "{random values}"
      To: Blob = ""{random values}""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates\CA\Certificates\E5215D3460C2C20BBE2D9FE5FB665DAA2C0E225C
    • From: Blob = "{random values}"
      To: Blob = ""{random values}""

Step 5

Search and delete this file

[ Learn More ]
There may be some files that are hidden. Please make sure you check the Search Hidden Files and Folders checkbox in the "More advanced options" option to include all hidden files and folders in the search result.
  • %Windows%\nvsvc32.exe

Step 6

Restart in normal mode and scan your computer with your Trend Micro product for files detected as WORM_YAHOS.F. 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 7

Restore this file from backup only Microsoft-related files will be restored. If this malware/grayware also deleted files related to programs that are not from Microsoft, please reinstall those programs on you computer again.

  • %System Root%\ndl.dl
  • %System Root%\ntdl.dl
  • %Windows%\ndl.dl
  • %Windows%\ntdl.dl


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