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
Based on the settings of your F-Secure security product, it will either move the file to the quarantine where it cannot spread or cause harm, or remove it.
A False Positive is when a file is incorrectly detected as harmful, usually because its code or behavior resembles known harmful programs. A False Positive will usually be fixed in a subsequent database update without any action needed on your part. If you wish, you may also:
Check for the latest database updates
First, check if your F-Secure security program is using the latest updates, then try scanning the file again.
Submit a sample
After checking, if you still believe the file is incorrectly detected, you can submit a sample of it for re-analysis.
Note: If the file was moved to quarantine, you need to collect the file from quarantine before you can submit it.
Exclude a file from further scanning
If you are certain that the file is safe and want to continue using it, you can exclude it from further scanning by the F-Secure security product.
Note: You need administrative rights to change the settings.
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:
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