The complex piece of malware known as Gauss has a number of mysteries that have grabbed the attention of security researchers: Where did the attack tool originate, what is the function of the encrypted payload, and why does the malware focus on stealing financial data?
A fourth question popped up Aug. 10. Researchers found that the Gauss malware installs, for no obvious reason, a custom font called Palida Narrow. The font contains no malicious code and does not introduce a vulnerability into the victim's system, said Roel Schouwenberg, a senior researcher with security-software firm Kaspersky Labs, which first reported on the malicious program.
"We are currently at a loss," said Schouwenberg. "Perhaps the font is used as some sort of infection marker. We don't know."
Using such a marker, attackers could remotely check whether systems that browse to an attacker-controlled Website are infected by checking to see if the font is installed. Since the font had existed nowhere else, any system that had had the font installed likely encountered Gauss.
Defenders used the theory to create Websites that could detect the existence of the font marker and determine if a system had been compromised by Gauss. On Aug. 8, the Laboratory of Cryptography and System Security (CrySys) at the Budapest University of Technology and Economics stood up a Website that can detect the existence of the unique font, and thus the signs of a Gauss infection, just by a computer visiting the site.
The next day, Kaspersky followed suit.
"This standard behavior of the browsers makes it possible to enumerate all the fonts that are installed in your system, but particularly to pinpoint if Palida Narrow is installed," CrySys stated in a blog post. "Considering this case, if the Palida is installed, your browser will simply use it for rendering the Web page. If not, and only in that case, it will try to download" the file from our server.
Other possibilities for the font: It may be useful for hiding information within Web pages, or it could be a way to mark documents that were printed from an infected system, the university group stated.
Malware researchers believe that Gauss was created by the same development group as Flame, an espionage program thought to have spread to thousands of systems over at least a three-year period. Unlike its cousin, Gauss spread faster by an unknown means like infecting three or four times as many systems. While Flame gathered intelligence on and from the systems it infected, Gauss focuses more on surveying specific targets, and gathering financial data. It also carries an encrypted payload that will only execute on specific systems, according to Schouwenberg.
"All these things hint towards the creators going after an air-gapped network," said Schouwenberg. Military and other sensitive networks are typically cut off from the Internet, a configuration referred to as "air-gapped."
While the Gauss malware carries all the hallmarks of the same development program as Flame, it is only distantly related to Stuxnet and Duqu. U.S. administration officials acknowledged developing Stuxnet with the Israelis, according to a recent book.