Backdoor.Bofishy.B

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Discovered: October 20, 2002
Updated: February 13, 2007 11:59:00 AM
Also Known As: Unix/Backdoor-ADM [McAfee], UNIX_ALUTAPS.A [Trend], Backdoor.Linux.Bofishy.b [Kasp
Type: Trojan Horse
Systems Affected: Linux, UNIX


Backdoor.Bofishy.B is a backdoor Trojan horse that infects the Sendmail program. Infected versions of Sendmail create a backdoor process during the installation of Sendmail. This process attempts to contact the attacker's computer and give the attacker access to a shell on the local computer.

Antivirus Protection Dates

  • Initial Rapid Release version October 21, 2002
  • Latest Rapid Release version August 08, 2016 revision 023
  • Initial Daily Certified version October 21, 2002
  • Latest Daily Certified version August 09, 2016 revision 001
  • Initial Weekly Certified release date October 23, 2002

Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

Writeup By: Frederic Perriot

Discovered: October 20, 2002
Updated: February 13, 2007 11:59:00 AM
Also Known As: Unix/Backdoor-ADM [McAfee], UNIX_ALUTAPS.A [Trend], Backdoor.Linux.Bofishy.b [Kasp
Type: Trojan Horse
Systems Affected: Linux, UNIX


Backdoor.Bofishy.B is a patch for the source code of Sendmail 8.12.6. The version of the Sendmail distribution that is infected with the Trojan includes the file t-shm.c, which is modified to create the backdoor process.

The t-shm.c file is part of a test suite that is compiled and executed during the installation of Sendmail. It is compiled to a binary file named t-shm. When t-shm is executed, it creates and executes a shell script named "test".

This script first drops a C program named conftest.c, compiles it under the name of the current user's shell, and then executes it. The conftest.c program connects to the IP address 66.37.138.99 on port 6667/tcp and accepts commands from an attacker. One command opens a shell for the attacker on the compromised computer.

The script then patches the source of Sendmail to remove the source code of the backdoor from t-shm.c, deletes the backdoor binary, and deletes itself. However, remnants of the backdoor code are still visible in t-shm.c, and the binary t-shm still contains the backdoor.

Additional information
If you downloaded and used version 8.12.6 of Sendmail, you may be at risk. To determine whether your version of Sendmail contains or contained the Trojan, look in the t-shm.c file under the libsm/directory of the Sendmail source code tree. If this file contains the string "sm_base64_data", this indicates the presence of the backdoor. In addition, if the last two lines of the file are exactly the following:

unsigned char sm_base64_data[] = {
};

(that is, if the sm_base64_data array is empty)

then it indicates that the backdoor was successfully run on the computer. Reboot the computer to make sure that the backdoor process is no longer present in memory.

If you determine that you have a version of Sendmail that contained the Trojan, download a clean distribution of Sendmail, verify its integrity by checking the cryptographic signature of the package, and reinstall it on your system.

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: Frederic Perriot

Discovered: October 20, 2002
Updated: February 13, 2007 11:59:00 AM
Also Known As: Unix/Backdoor-ADM [McAfee], UNIX_ALUTAPS.A [Trend], Backdoor.Linux.Bofishy.b [Kasp
Type: Trojan Horse
Systems Affected: Linux, UNIX


NOTE: These instructions are for all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

  1. Update the virus definitions.
  2. Run a full system scan, or recompile all files that are detected as Backdoor.Bofishy.B.

For details on how to do this, read the following instructions.

To update the virus definitions:
All virus definitions receive full quality assurance testing by Symantec Security Response before being posted to our servers. There are two ways to obtain the most recent virus definitions:
  • Run LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions are posted to the LiveUpdate servers one time each week (usually Wednesdays) unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, look at the Virus Definitions (LiveUpdate) line at the top of this write-up.
  • Download the definitions using the Intelligent Updater. Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). They must be downloaded from the Symantec Security Response Web site and installed manually. To determine whether definitions for this threat are available by the Intelligent Updater, look at the Virus Definitions (Intelligent Updater) line at the top of this write-up.

    Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.

To scan for and delete the infected files:
  1. Start your Symantec antivirus program, and make sure that it is configured to scan all files.
  2. Run a full system scan.
  3. If any files are detected as infected with Backdoor.Bofishy.B, delete or recompile them.


Writeup By: Frederic Perriot