Pierluigi Paganini December 07, 2012

Zeus, a name that security experts know very well, it’s one of the most prolific and dangerous malware of the history. In the years several versions have been detected, it’s one of the first malware for which it has been applied an excellent business model that made possible its evolution in cybercrime, unique constant is the monetization process based on the exploit of bank accounts.

Last version detected of Zeus botnet has been successful in the theft of about $47 million from European banking customers in the past year according revelation of security experts from Check Point and Versafe that discovered a sophisticated offensive.

The researcheres discovered a multi-dimensional and targeted attack, named “Eurograbber”, that stole an estimated 36+ million Euros from more than 30,000 bank customers from multiple banks across Europe. The attacks were originated in Italy and rapidly spread to other countries of UE such as Spain, Germany and Holland.

The attack described in a report released by the security vendors was based on the diffusion of a malware, directed at PCs and mobile devices, that is able to defeat the two-factor authentication process implemented by banks by intercepting bank messages sent to victims’ phones.

The attacks have exploited Android and Blackberry OSs confirming the great interest of cybercrime in the use of new channels, such as mobile and social media,  to spread cyber threats. The malware has been designed to attack wide audience infecting both corporate and private banking users and illicitly transfer funds out of customers’ accounts in amounts ranging from 500 to 250,000 Euros each.

The schema of attacks is usual, the victim clicks on a malicious link received via an email as part of a phishing attempt,  installing customized variants of the Zeus, SpyEye, and CarBerp Trojans. Infection could also  happens either during internet browsing or clicking on a link inside a social network.

During first visit to bank web site the malware intercepts the dialogue requesting to the user to enter a valid mobile phone number for authentication purpose and to validate successive transactions.  Eurograbber would offer a “banking software security upgrade” that would infect victims’ phones with the mobile version of Zeus, ZITMo (Zeus in the mobile”)  that is equipped with a function to intercept the bank’s sms message that include bank’s transaction authorization number (TAN).

In the following picture is proposed the SMS message (Italian ver.) sent to an Italian customer’s mobile device that contains a malicious link to the upgrade for the online banking security software. Clicking on this link user installs the Eurograbber Trojan on the his mobile device.

“Simultaneous with the SMS being sent to the bank customer’s mobile device, the following message appears on the customer’s desktop instructing them to follow the instructions in the SMS sent to their mobile device in order to upgrade the system software to improve security”

To improve security of the operations, banking implemented a 2-factor authentication mechanism validating identity of the clients and the integrity of transactions with introduction of a special code. When the bank customer starts an online banking transaction, the bank sends a TAN via SMS to the customer’s mobile device. The customer then confirms and completes operation entering the TAN code in the online form proposed by banking service.

Once capture the TAN number the malicious code is able to steal funds from victim’s bank account. The collections of infected machines is managed by an efficient Command & Control (C&C) server infrastructure described in the report:

“In order to facilitate such a sophisticated, multi-stage attack, a Command & Control (C&C) server infrastructure had to be created. This infrastructure received, stored and managed the information sent by the Trojans and also orchestrated the attacks. The gathered information was stored in an SQL database for later use during an attack. In order to avoid detection, the attackers used several different domain names and servers, some of which were proxy servers to further complicate detection. If detected, the attackers could easily and quickly replace their infrastructure thus ensuring the integrity of their attack infrastructure, and ensuring the continuity of their operation and illicit money flow.”

To date, this schema of attacks have been reported only for European institurions but it could potentially affect banks all over the wolrd.

The attack demonstrates that not only desktop PCs have to be protected by security systems but also mobile needs countermeasures to mitigate cyber threats, report states:

“To best protect against attacks like Eurograbber, online banking customers need to ensure they have the most current protection in two areas – on the network that provides them internet access to their bank and on the computer they use to conduct online banking.”

Pierluigi Paganini