September 4, 2012 By Amit Klein 2 min read

IBM has discovered a new Tatanga attack against chipTAN systems used by banks in Germany, which generates unique transaction authentication numbers (TAN). These systems require that the bank card for the account be inserted in the device to generate a TAN that is specific to the current transaction.

How the Attack Bypasses chipTAN Systems

Tatanga checks the user account details, including the number of accounts, supported currencies and balance/limit details. It then chooses the account from which it could steal the highest amount. Next, it initiates a transfer. At this point, Tatanga uses a webinject to trick the user into believing that the bank is performing a chipTAN test. The fake instructions request that the user generate a TAN for the purpose of this “test” and enter the TAN.

These are the instructions through which it steals user information, as they appear in German:

Stecken Sie Ihre Chipkarte in den TAN-Generator und drücken “F.” Halten Sie den TAN-Generator vor die animierte Grafik. Dabei müssen die Markierungen (Dreiecke) von der Grafik mit denen auf Ihrem TAN-Generator übereinstimmen. Prüfen Sie die Anzeige auf dem Leserdisplay und drücken “OK.” Prüfen Sie die Hinweise (Empfänger-Kontonummer (ohne führende Nullen), Bankleitzahl des Empfängers und Betrag) auf dem Leserdisplay und bestätigen diese dann jeweils mit “OK” auf Ihrem TAN-Generator. Hinweis: Uberprufen Sie die Anzeige des TAN-Generators immer anhand der Original-Transaktions-Daten – z.B. einer Rechnung.

Translated to English, the text reads:

Insert your smart card into the TAN generator and press “F.” Place the TAN generator next to the animated graphic on your computer screen. Here, the markings (triangles) of the graph correspond to those on your TAN generator. Check the display on the reader display, and press “OK.” Check the transaction details (recipient’s account number, recipient’s bank and amount of the transfer) on the reader screen and then confirm by clicking “OK” on your TAN generator. Note: Also check the display of the TAN generator always using the original transaction data — for example, an invoice.

Tatanga then captures the TAN entered by the user at the bank site and proceeds to make a transaction in the background. Meanwhile, it replaces the user transaction history/balance details to hide the fraudulent activities from the victim.

The Need for Endpoint Protection

ChipTAN systems are considered fairly secure because the generated TAN takes into account both transaction details and the bank-issued chip and PIN card. However, this attack demonstrates that by using Man in the Browser (MitB) social engineering techniques, financial malware can circumvent chipTAN security. Implementing endpoint protection against advanced malware like Tatanga, Zeus and others is the only way to make sure the integrity of second-factor security measures like chipTAN are not compromised.

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