Thu, 02/19/2009 - 11:47 — Igor Donchenko
The FortiGuard Global Security Research Team has investigated the case of a new mobile worm resorting to a breakthrough propagation strategy, which leverages SMS messages and Internet access.
This new worm, deemed SymbOS/Yxes.A!worm (also known as "Sexy View"), is targeting mobile devices running SymbianOS S60 3rd Edition (eg: Nokia 3250), but may run on a wider range of devices, as it has been reported to function on phones operating SymbianOS S60 3rd edition FP 1 (eg: Nokia N73). It bears a valid certificate signed by Symbian, and installs as a valid application on factory mobile devices running S60 3rd Edition.
It gathers phone numbers from the infected device's file system, and repeatedly attempts to send SMS messages to those. The messages feature a malicious Web address (URL); upon "clicking" on the address in the received message, the recipients will download a copy of the worm (provided their phones/subscriptions allow for internet browsing).
Beyond propagating to as many users as possible via the strategy mentioned above, the worm's aim is to gather intelligence on the infected victim (such as serial number of the phone, subscription number) and post it to a remote server likely controlled by cyber criminals. Whatever the latter may do with such information is unknown as of writing.
It must be noted that due to its propagation strategy relying on the worm copy being hosted on a web server, the worm can mutate easily. According to Guillaume Lovet, senior manager of Fortinet's Threat Research Team, "As far as our analysis goes, the worm currently does not take commands from the remote servers it contacts. However, since the copies hosted on the malicious servers are controlled by the cyber criminals, they may update them whenever they want, thereby effectively mutating the worm, adding or removing functionality. We're really at the edge of a mobile botnet here."
The Yxes mobile worm is reported to be currently spreading in the wild. Caution should always be taken when opening attachments and following URL's received through messages (SMS/MMS). In the case of an infection, please contact your service provider.