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Trojan:SymbOS/Skulls.C

Classification

Category: Malware

Type: Trojan

Platform: SymbOS

Aliases: Skulls.C, SymbOS/Skulls.C

Summary


Skulls.C is a variant of SymbOS/Skulls.A trojan, which has similar functionality to the Skulls.A but uses different files.

Skulls.C is a malicious SIS file trojan that replaces the system applications with non-functional versions, drops SymbOS/Cabir.F worm in to the phone and disables third party applications that could be used to disinfect with such as FExplorer, EFileman.

Removal


Disinfection with two Series 60 phones

Download F-Skulls tool from our FTP server to your computer or to a clean phone, then:

  • 1. Install F-Skulls.sis into infected phones memory card with a clean phone
  • 2. Put the memory card with F-Skulls into infected phone
  • 3. Start up the infected phone, the application menu should work now
  • 4. Go to application manager and uninstall the SIS file in which you installed the skulls variant
  • 5. Download and install F-Secure Mobile Anti-Virus to remove any Cabirs dropped by the Skulls variant
  • https://www.europe.f-secure.com/estore/avmobile.shtml or with mobile itself https://mobile.f-secure.com
  • 6. Remove the F-Skulls with application manager as the phone is now cleaned
Knowledge Base

Find the latest advice in our Community Knowledge Base.

About the product

See the manual for your F-Secure product on the Help Center.

Contact Support

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Submit a sample

Submit a file or URL for further analysis.

Technical Details


Skulls.C tries to disable F-Secure Mobile Anti-Virus by replacing it's files with non-functional versions. However as F-Secure Mobile Anti-Virus is capable of detecting Cabir.F contained by Skulls using generic detection. The Anti-Virus will detect the infected SIS file and prevent it from being installed. Provided that the Anti-Virus is in realtime scan mode as it is by default.

The Cabir.F worm dropped by Skulls.C is already detected with generic detection as Cabir.Gen. So the Skulls.C is already detected and stopped without need for updated Anti-Virus database.

The Cabir.F dropped by Skulls.C does not activate automatically, and will not activate on reboot. The only way the dropped Cabir worm can activate is if user goes to the icon of the dropped Cabir file and run it from there.

The Original Skulls.C SIS file is named "Skull.sis". Unlike Skulls.A, the Skulls.C variant does not show any pop-up messages during install (except the "Installation security warning - unable to verify supplier" message shown by the operating system).

Like Skulls.A the Skulls.C replaces the application icons with skull icon, this time so that each replaced application has caption "Skulls"

If Skulls.C is installed only the calling from the phone and answering calls works. All functions which need some system application, such as SMS and MMS messaging, web browsing and camera no longer function.

If you have installed Skulls.C, the most important thing is not to reboot the phone and follow the disinfection instruction in this description.

Installation to system

Like Skulls.A Skulls.C is a SIS file that installs critical System ROM binaries and Cabir.F worm into C: drive. The System ROM files are installed with exact same names and locations as in the ROM drive.

Symbian operating system has a feature which causes any file that is in C: drive replace file in ROM drive with identical name and location.

Spreading in: Skull.sis

Payload

Replaces built in applications with non-functional ones and installs Cabir.F worm.