Home / malware Trojan-Downloader:JS/Gumblar.X
First posted on 09 January 2010.
Source: SecurityHomeAliases :
There are no other names known for Trojan-Downloader:JS/Gumblar.X.
Explanation :
A trojan that secretly downloads malicious files from a remote server, then installs and executes the files.
Additional DetailsTrojan-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.
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:
€ http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-2992Last update 09 January 2010
