Home / malware Trojan-Downloader:W32/Oficla
First posted on 08 July 2010.
Source: SecurityHomeAliases :
Trojan-Downloader:W32/Oficla is also known as w32_sasfis.e259!tr (Other), Trojan.Sasfis (Symantec).
Explanation :
This type of trojan secretly downloads malicious files from a remote server, then installs and executes the files.
Additional DetailsTrojan-Downloader:W32/Oficla identifies a family of malware that are distributed as attachments to fake e-mail messages.
On installation, the trojan-downloader connects to a remote server and downloads additional files (which are mostly malicious) onto the system. The specific files downloaded will vary depending on the variant.
A representative example of Oficla variant is:
€ Trojan-Downloader:W32/Oficla.AE
Distribution
Oficla variants are distributed as executable or zipped files attached to misleading e-mail messages. Some of the most common messages used to deliver this trojan involve fake offers for iTunes Gift certificates or for Amazon.com orders, UPS invoice other attachments are disguised as resumes.
The text in the e-mail message entices the unsuspecting user to open the attached executable; Oficla's actual malicious code is packed (using a custome packer) in a DLL file secretly embedded in the executable file.
Installation
Once the attached executable file is launched by the user, it will extract the DLL file into the Windows temporary folder.
The DLL file is saved, usually with the 1.tmp filename:
€ %Temp%\1.tmp
During installation, the 1.tmp file will be executed and injected to a normal process. Subsequently, when running under the normal process it will create a file in the Windows system folder.
The created file uses a somewhat non-standrd extension file, for example:
€ %windir%\system32\fjof.sto
Note: The filename and extension name may change from variant to variant.
Registry Changes
In order for it to automatically start on restart, it modifies the registry:
€ HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
Shell = Explorer.exe
to
€ HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
Shell = Explorer.exe rundll32.exe [Oficla_dll file] ["parameter"]
Example of a modified registry entry:
€ HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
Shell = Explorer.exe rundll32.exe fjof.sto vffwdLast update 08 July 2010
