Security Experts:

Hybrid Trojan "GozNym" Targets North American Banks

Researchers at IBM Security have come across a hybrid Trojan that is a combination between the Nymaim dropper and the Gozi financial malware.

Dubbed by IBM “GozNym,” the threat has been used to target 22 financial institutions in the United States and two in Canada. The malware has been used in attacks aimed at banks, credit unions, e-commerce platforms, and retail banking. While the campaign only started this month, IBM believes the attackers have already stolen millions of dollars from victims.

Nymaim has been mainly known as a dropper used to deliver ransomware, including its own police-themed screen locker, which blocks computers and instructs victims to pay a “fine”.

Researchers believe that the developers of Nymaim, a stealthy threat that includes efficient evasion techniques, recompiled the malware’s source code with code taken from Gozi ISFB, a variant of the well-known banking Trojan that was spotted targeting Swiss users earlier this year. Gozi’s source code was leaked on two occasions over the past years.

“We know that Gozi is still very active in the underground, and even some of its authors are actively being investigated by law enforcement agencies. They have changed their model and sell some specific modules to different malware projects,” Andrew Komarov, chief intelligence officer at InfoArmor, told SecurityWeek. “You may see posts about ‘Gozi for rent’ for $400 per week, supporting WEB-injects for Chrome, IE, Firefox, and have modules similar to well-known online banking Trojans like Zeus and SpyEye (VNC, keylogger – used for successful online-banking theft).”

Until November 2015, Nymaim was primarily used as a ransomware dropper, but towards the end of the year IBM X-Force researchers noticed that the malware had started fetching a Gozi ISFB web injection module and using it to launch online banking attacks.

The threats were combined into a single piece of malware in early April, with Nymaim being launched in the first stage of deployment and the Gozi ISFB component in the second stage.

“The new GozNym hybrid takes the best of both the Nymaim and Gozi ISFB malware to create a powerful Trojan. From the Nymaim malware, it leverages the dropper’s stealth and persistence; the Gozi ISFB parts add the banking Trojan’s capabilities to facilitate fraud via infected Internet browsers,” explained Limor Kessem, executive security advisor at IBM.

The GozNym sample analyzed by IBM is currently detected by most major antivirus vendors based on its signature.

“Unfortunately, the leak of source codes of famous online banking Trojans created a new market with modifications and different variations, but they are based on exactly the same principles as several years ago. Security bypass and AV evasion mechanisms are rapidly changing due to the efforts of the security community, this is why those bad actors are looking for new and private zero-day exploits for modern platforms and specific security solutions,” Komarov said.

Related: New GM Bot Version Released After Source Leak

Related: Gozi Banking Trojan Targets Windows 10's Edge Browser

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Eduard Kovacs is an international correspondent for SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.