Security researchers have warned that cybercrooks might be able to compromise online bank accounts even in cases where banks use SMS messages to authorise transactions.
The approach relies on first compromising a targeted user's computer using a variant of the ZeuS banking Trojan before infecting the same user's smartphone. Thereafter it would be possible to initiate a transaction and authorise it following the receipt of an SMS message to a second compromised device.
The so-called ZeuS Mitmo (man-in-the-mobile) attack is explained in a blog post by David Barroso, of S21sec e-crime. The approach first relies on tricking a user into getting infected by Zeus on the desktop, perhaps via use of a targeted email that points to a booby-trapped website or contains an infected attachment. Thereafter a user's login credentials are captured next time the mark logs into an online banking site.
The malware then generates a fake dialog box that attempts to trick the victim into disclosing the number and manufacturer of his or her mobile phone. This phone would then be sent a fake security certificate, which is actually a malicious banking Trojan tailored to the target's smartphone (this can be either Symbian or BlackBerry).
This malicious mobile application then monitors all incoming SMS as well as installing a backdoor to receive commands via SMS, from a designated command and control number, which can be altered. Samples of a malicious application for Nokia that works alongside Zeus to carry out the attack are analysed by S21sec here.
The approach is plausible if a little convoluted but the added complexity may be worth it in targeted attacks, perhaps against organisations or wealthy individuals whose banks use SMS notification for two factor authentication of transactions.
Luis Corrons, technical director of PandaLabs confirmed that the malware behind the attack is real and not just a theoretical risk. Victims trying to deny making a disputed transaction where SMS confirmation has been applied are liable to be in for all sorts of trouble, a factor that makes the attack particular insidious. ®