09 July 2005

Very interesting pair of trojans
SymbOS/Onehop.A and SymbOS/Bootton.A

Onehop.A in action

NAME: Onehop.A
ALIAS: SymbOS/Onehop.A

Onehop.A is a Symbian SIS file trojan that causes device to reboot when trying to use system applications and sends copies to SymbOS/Bootton.A trojan to first device it finds with bluetooth.

In its structure Onehop.A is quite similar to Skulls family trojans. With the exception that instead of replacing system files with corrupted binaries,the Onehop.A uses application that causes device to reboot.

Thus if a device is infected with Onehop.A, pressing menu button or any system application button the device immediately reboots.

Onehop.A disables most of critical system functions and third party file managers, so that even if the device wouldn't immediately reboot it is still unusable before it is disinfected.

In addition of disabling applications on the phone, uses a modified version of cabir as distribution component for SymbOS/Bootton.A. So that first phone that is found over bluetooth receives Bootton.A over bluetooth if the user accepts connection. The modified Cabir that Onehop.A infects the device with is incapable of spreading, so it is detected as component of Onehop.A not as separate malware.

Like Skulls.A the Onehop.A replaces the application icons with it's own icon, this time the icon is a heart icon with the text "I-Love-U"

Disinfection with two Series 60 phones

Download F-Skulls tool from ftp://ftp.f-secure.com/anti-virus/tools/f-skulls.zip or directly with phone http://www.europe.f-secure.com/tools/f-skulls.sis

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. Press menu button until you get Symbian process menu, look for any applications with heart icon. Kill the application processes with 'C' button.
5. Go to application manager and uninstall the SIS file in which you installed the Onehop.A
6. Download F-Secure Mobile Anti-Virus from http://phoneav.com and activate the Anti-Virus
7. Scan the phone and remove any remaining components of Onehop.A
8. Remove the F-Skulls with application manager as the phone is now cleaned

Installation to system Onehop.A is a SIS file that installs small component that resets the device if executed, this component is installed into locations where it replaces system and third party applications.

Spreading in PhotoID.v3.06_NEW_7610_3230_6630_SMPDA.sis

Payload Replaces built in and third party applications with component that causes device to reboot when executed.

Uses modified Cabir to spread SymbOS/Bootton.A. The Cabir that Onehop.A is modified so that instead of sending a copy of itself that it generates at startup. The modified cabir loads SIS file installed by Onehop.A into a location where Cabir expects to find it's own SIS file and starts sending it.

Thus instead of sending copies of itself the modified Cabir sends copies of SymbOS/Bootton.A. The modified Cabir that Onehop.A uses is based on Cabir.B and contains the same replication but as Cabir.B, and is thus capable of sending SymbOS/Bootton.A only to the first phone it finds after reboot.

Generic detection that detects Onehop.A was published for F-Secure Mobile Anti-Virus on November 19th, 2004 in database build number 11.

Exact detection for Onehop.A was published for F-Secure Mobile Anti-Virus on July 8th, 2005 in database build number 44.

F-Secure Corporation