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[轉貼]Linux系統陷阱木馬..
« 於: 2003-09-03 11:35 »
The Trojan.Linux.JBellz Trojan horse arrives as a malformed .mp3 file. When the .mp3 file is played with a specific version of the mpg123 player under Linux, the code of the Trojan horse is executed; thereby, deleting all the files in the home directory of the current user.


technical details

Trojan.Linux.JBellz exploits a vulnerability in the mp3 frame header, which decodes the mpg123 player. When a malformed mp3 file containing Trojan.Linux.JBellz triggers the vulnerability in the player, a shell code is executed. The code removes all the files in the current user's home directory (~), recursing into subdirectories.

Version pre0.59s of the mpg123 player has been verified to be vulnerable. This bug ostensibly does not affect previous versions of the player.

The current version of Trojan.Linux.JBellz is designed to affect the following Linux systems only:

    * Suse 8.0
    * Slackware 8.0


NOTE: The Trojan may affect other Linux systems, and modifying the Trojan is easy enough to support other Linux distributions, or other platforms.

recommendations

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

    * Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
    * If a blended 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.
    * 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.
    * Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
    * Isolate infected computers quickly to prevent further compromising your organization. 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.

removal instructions

The following instructions pertain to 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 and delete all the files detected as Trojan.Linux.JBellz.


For specific details on each of these procedures, read the following instructions.

1. Updating the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:

    * Running LiveUpdate, which is the easiest way to obtain the virus definitions: These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate), in the "Protection" section, at the top of this writeup.
    * Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater), in the "Protection" section, at the top of this writeup.

      The 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.


2. Scanning for and deleting the infected files

   1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
          * For Norton AntiVirus consumer products: Read the document, "How to configure Norton AntiVirus to scan all files."
          * For Symantec AntiVirus Enterprise products: Read the document, "How to verify that a Symantec Corporate antivirus product is set to scan All Files."
   2. Run a full system scan.
   3. If any files are detected as infected with Trojan.Linux.JBellz, click Delete.


Additional information:

Symantec antivirus products detect the tool used to create the malformed .mp3 files, which contain Trojan.Linux.JBellz, as Trojan.Linux.JBellz.dr.

Additional information about the vulnerability described in this writeup can be found in the message that was posted to the SecurityFocus Bugtraq forum, at:http://online.securityfocus.com/archive/1/306476.


Write-up by: Frederic Perriot


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