Tinba: World’s Smallest Malware Has Big Bag of Nasty Tricks

IBM Security Trusteer researchers have recently discovered an infection campaign using a new variant of the banking Trojan Tinba that targets European banking customers. The latest version has been enhanced with several capabilities that significantly improve the malware’s effectiveness and resiliency.

Small and Free of Charge

Tinba is a truncation of “tiny banker” and, when first discovered in 2012, was the smallest banking Trojan in circulation by file size.

Tinba’s destiny took an interesting turn when its source code was publicly leaked in July 2011 in an apparent dispute between rival cybercriminals. Since the leak, various gangs have been able to rework the ready-made malicious code at no cost.

Security Intelligence reported in September of last year that, as a result of the proliferation of the source code, several campaigns using Tinba variations were launched in countries around the world, in many cases sporting significant improvements to the original code.

Latest European Tour

In May 2015, IBM Security Trusteer researchers discovered a Tinba infection campaign targeting Poland, Italy, the Netherlands and Germany. Nearly half of the recognized incidents were focused on Poland, with 45 percent of the security events able to be traced back to the country. Italy was a distant second at 21 percent, according to the research.

Latest Tinba camgain targets distributed per country

Credential Stealing and Fake Messages

When Tinba infects a computer and the user tries to log in to one of the targeted banks, Tinba’s webinjects are launched into action. Depending on the targeted bank, victims are presented with fake messages and Web forms asking for personal information, login credentials or requests to perform a funds transfer. The notice may even attempt to convince users that money has been added to their account accidentally and must be refunded immediately.

Victim is presented with a fake message while browsing the banks web-site

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Tinba’s Fallback Mechanisms

In line with Trojan anti-research and resilience features, the author of this Tinba variation, wary of potential hijacking and takedowns, incorporated several fallback mechanisms to make sure the botnet remains intact. These safeguards include:

  • Public key signing to ensure that bot commands and updates can only come from the authorized botmaster;
  • Bots authenticating the updating server before accepting a new configuration;
  • A machine-dependent encryption layer for each bot to prevent security researchers from spoofing bots;
  • Bots communicating with hard-coded resource URLs and fallback to DGA-made URLs when necessary.

The Globalization of the Malware Threat

This latest Tinba campaign is just one of many malware threats that have migrated to Europe after previously targeting U.S. banks. Cybercriminals such as the Dyre gang have been able to overcome language barriers and adapt their tactics to attack local banks. While this trend may prove a challenge to many banks who have not yet hardened their defenses, it also provides an opportunity for those institutions to take advantage of the lessons learned having combated this malware elsewhere.

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Ori Bach

Senior Security Strategist, Trusteer

Ori Bach is a product and risk management expert with 12 years of expertise in the financial services fraud and compliance space. He currently serves as Senior Security Strategist at IBM-Trusteer. Ori previously worked at NICE–Actimize for 9 years as Director of Solutions Management, where he helped oversee various aspects of company’s fraud and case management solutions. Ori has an LLB degree from Tel-Aviv University and is a member of the Israeli BAR association. Ori's special areas of interest are analytics and the interdependencies between risk management and customer experience.