Zeus Trojan opens backdoor crack to two-factor SMS authentication

Zeus Trojan opens backdoor crack to two-factor SMS authentication

Security researchers are warning of a new threat to bank SMS two-factor authentication systems that combines social engineering and a variant of the Zeus Trojan to hijack user mobile phones during the online banking session.

The attack is described in a blog post by David Barroso of e-crime outfit S21sec. The post hypothesises a scenario in which an infected user PC is redirected to a bogus site and asked for mobile phone number, make and model alongside the usual banking credentials. The user is then sent an SMS message with a link to download a malicious application under the guise of installing a new security certificate.

The application that the user installs will monitor all the incoming SMS and open a backdoor to receive commands via SMS. Barroso demonstrates how this can be achieved via the Symbian S60 application, which has the name 'Nokia update'.

The attacker now has all the user credentials necessary to loot a two-factor protected bank account, notes Barroso:

  • The attacker logs in with the stolen credentials using the user's computer as a socks/proxy and performs a specific operation that needs SMS authentication
  • An SMS is sent to the user's mobile device with the authentication code. The malicious software running in the device forwards the SMS to other terminal controlled by the attacker
  • The attacker fills in the authentication code and completes the operation.

"We are working with mobile carriers to help them to detect infected devices," says Barroso. "Mobile carriers are the key actors in this incident, just because they are the only ones that can detect which devices are infected and block all the connections to/from the mobile C&C."

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