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Trojan-Downloader:JS/Gumblar.X

Classification

Category: Malware

Type: Trojan-Downloader

Aliases: Trojan-Downloader:JS/Gumblar.X

Summary


Trojan-Downloader:JS/Gumblar.X drops a malicious file that injects malicious JavaScript code into a website's pages or a user's web browser; which in turn exploits a PDF vulnerability to redirect users to malicious websites.

Removal


Automatic action

Based on the settings of your F-Secure security product, it will either automatically delete, quarantine or rename the detected program or file, or ask you for a desired action.

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Technical Details


The trojan's code is obfuscated using string substitutions. During much of the first half of 2009, as this malware became more widespread, its author(s) replaced the original code with more complex, dynamically generated code to make it harder for security programs to detect.Gumblar infections constituted one of the major threats of 2009. It is named after the domain (gumblar.cn) it first used to infect visitors to the site; it has since switched to other domain names. The major distribution sites have since been shut down, but infected sites that are not properly cleaned may still be active.

Distribution

Websites may be infected when the attacker gains stolen FTP credentials. Gumblar.X infections were widely seen on systems running the following operating systems:

  • Microsoft Windows XP SP2
  • Microsoft Windows 2000 Advanced Server
  • Microsoft Windows 2003 Standard

Compromised webserver will have webpage(s) that redirect to malicious webservers.

Installation

On execution, Gumblar.X drops malicious files on the system. These files are typically encrypted; the decryption is based on the cipher key's character indexes.Some representative dropped files are:

  • C:\\RECYCLER\\iexplore.exe - dropped in the Recycle bin
  • C:\Documents and Settings\All Users\Start Menu\Programs\Startup\Uninstall.exe - dropped in the Startup folder

The shell code dropped by the trojan uses a PDF vulnerability to redirect the user's browser to a malicious website. For more information about the vulnerability, please see:

Date Created: -

Date Last Modified: -