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  3. Trojan.Silentbanker

Trojan.Silentbanker

Risk Level 1: Very Low

Discovered:
December 17, 2007
Updated:
January 8, 2008 12:54:17 PM
Also Known As:
Spy-Agent.cm [McAfee]
Type:
Trojan
Infection Length:
54,189 bytes and 98,304 bytes
Systems Affected:
Windows 2000, Windows 95, Windows 98, Windows Me, Windows NT, Windows Server 2003, Windows Vista, Windows XP
The Trojan may be downloaded or delivered silently through Web exploits and then executed. It arrives as the following file:
sk.exe

It then drops a dll file with the following file name pattern and then deletes itself:
[RANDOM CHARACTERS][RANDOM DIGITS].dll

At the time of writing, the following file names have been observed:
  • appmgmt14.dll
  • dbgen47.dll
  • drmsto34.dll
  • faultre66.dll
  • kbddiv55.dll
  • kbddiv79.dll
  • msisi83.dll
  • msvcp793.dll
  • msvcr25.dll
  • nweven2.dll
  • pngfil51.dll
  • pschdpr89.dll
  • versio40.dll
  • wifema85.dll
  • winstr21.dll
  • wzcsv64.dll


The Trojan drops additional randomly named files in the %System% folder to hold configuration information and to log information.

The Trojan also creates the following file which contains a list of all other file names that the threat uses:
%System%\[RANDOM CHARACTERS][RANDOM DIGITS].cpl

It creates the following registry entry so that it runs when an application calls for a sound device:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Drivers32\"midi1" = "[RANDOM CHARACTERS][RANDOM DIGITS].dll"

Note: This may have the side effect of disabling your sound device.

The Trojan may also add itself as a Browser Helper Object (BHO) in Internet Explorer by creating the following registry subkey:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Browser Helper Objects\{[RANDOM CLSID]}

It also creates the following registry entries:
  • HKEY_CLASSES_ROOT\CLSID\{[RANDOM CLSID]}\InprocServer32\(Default Value) = "[RANDOM CHARACTERS][RANDOM DIGITS].dll"
  • HKEY_CLASSES_ROOT\CLSID\{[RANDOM CLSID]}\TypeLib\(Default Value) = {[RANDOM CLSID]}
  • HKEY_CLASSES_ROOT\CLSID\{[RANDOM CLSID]}\(Default Value) = "[RANDOM CHARACTERS][RANDOM DIGITS]"

The Trojan targets many different banks using various methods in order to perform the following:
  • Gain access to accounts
  • Divert transactions to attacker controlled accounts


The Trojan performs the following actions:
  • Redirects legitimate requests to attacker controlled computers
  • Alters the HTML of pages shown to the user
  • Alters requests sent by the user to the bank
  • Captures screen shots of Web sites where the user must click instead of type the password
  • Sends full pages received by the victim to the attacker
  • Downloads new versions of itself
  • Downloads new configuration files
  • Records user names and passwords
  • Records the content of the clipboard
  • Steals cookies, digital certificates, and Adobe .sol files
  • Sends a list of all software installed on the compromised computer to the attackers


The threat hooks APIs in the following browsers:
  • Internet Explorer
  • Firefox


It may also hook APIs to the following file:
explorer.exe

The Trojan hooks the following APIs in order to intercept traffic received to and sent by the browser:
  • Send
  • Connect
  • CryptDeriveKey
  • CryptImportKey
  • CryptGenKey
  • HttpOpenRequestW
  • InternetReadFileExA
  • InternetReadFileExW
  • CommitUrlCacheEntryA
  • InternetReadFile
  • InternetQueryDataAvailable
  • HttpOpenRequestA
  • HttpSendRequestA
  • HttpSendRequestW
  • GetClipboardData
  • DispatchMessageA
  • DispatchMessageW
  • ExitProcess


Next, it downloads compressed and encrypted configuration files from the Trojan’s control server. These configuration files contain the following information:
  • URLs to change the HTML
  • HTML to find on targeted pages
  • HTML to be inserted/deleted/replaced on targeted pages
  • URLs to redirect to attacker sites
  • URLs to target for stealing account information
  • URLs to take screen shots from
  • Keywords to search for
  • Domain names to monitor and send to the attacker
  • Location of control servers
  • Location of updated Trojan executable
  • Location to send all stolen data
  • Porn URLs
  • Various other configuration data


The Trojan creates the following mutex so only one instance of the threat is running:
nnfbytsb3y

The Trojan may attempt to access the following Web sites:
  • iloveie.info
  • screensaversfor-fun.com
  • webcounterstat.info
  • reservaza.com
  • mystabcounter.info
  • microcbs.com
  • 85.255.119.218
  • 209.123.181.63


It may change the users DNS settings to the following attacker settings:
  • 85.255.116.133
  • 85.255.112.87


The Trojan then sends the collected information to the following remote locations:
  • microcbs.com
  • reservaza.com

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
  • Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
  • Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.
Writeup By: Liam O Murchu
Summary| Technical Details| Removal

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