Small.DAM arrives on the system as an attachment file to spam e-mails.

Here's a sample of an e-mail:



It may use any of the following strings as its Subject:

• 230 dead as storm batters Europe.
• A killer at 11, he's free at 21 and...
• British Muslims Genocide
• Naked teens attack home director.
• U.S. Secretary of State Condoleezza Rice has kicked German Chancellor Angela Merkel

Attachments may be any of the following filenames:

• Full Clip.exe
• Full Story.exe
• Read More.exe
• Video.exe

Small.DAM drops the following files upon execution:

• %SysDir%wincom32.sys - Kernel mode driver component
• %SysDir%peers.ini - Initialization file component
  

It also installs itself as a service with the name "wincom32" by creating the following registry keys:

• [HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServiceswincom32]
• [HKEY_LOCAL_MACHINESYSTEMCurrentControlSetEnumRootLEGACY_WINCOM32]

The kernel mode driver is an advanced payload injector. It carries a user-mode PE executable file and when the driver executes, it changes the services.exe process context and allocates new memory for the payload. It then copies the PE executable from kernel memory to the address space of services.exe and prepares the image for execution. Finally, it queues an Asynchronous Procedure Call (APC) for services.exe to execute the payload in its context.

This is the injected PE executable file trojan downloader in action and affected machines exhibits sending UDP packets with source port 4000 to IP addresses and destination ports taken from the decoded initialization file's "peers" section. The initialization file also maintains a "blacklist" section.

Additional information can be found from our weblog.

Last update 01 March 2007

 

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