More malware has been seen targeting a zero-day flaw in Internet Explorer that has already made its way into a popular crimeware toolkit.
The bug, which was discovered by Symantec, was linked last week to a backdoor Trojan known as Pirpi. However, researchers at FireEye have noted a Trojan named Hupigon is being used by attackers as well.
"At the moment, Hupigon is spreading through drive-by attacks primarily using the IE zero-day to infect systems," said Atif Mushtaq, senior security researcher at FireEye. "In the past, Hupigon has also been seen spreading through social engineering like through freeware/shareware software, free cracks, keygens and other methods."
Like Pirpi, Hupigon opens up a backdoor on infected systems and communicates to command and control servers. According to Mushtaq, some of the callback exploit servers were also found to have been involved in exploiting past zero-day bugs, such as a Microsoft Video ActiveX Control vulnerability back in 2009.
During the weekend, security researchers noted that the exploit had already made its way into the Eleonore exploit kit. Eleonore is one of the better known toolkits used by hackers, and "raises the stakes considerably," blogged Roger Thompson, chief research officer at AVG Technologies.
"What this means to Microsoft is that they should consider issuing an out-of-band patch," he blogged Sunday.
In May, McAfee Threat Researcher Francios Paget blogged that Version 1.3.2 of the toolkit sold for $1,200 in February. In July of 2009, Version 1.2 sold for $700 plus $50 for an encrypter, he wrote, adding that for $1,500, attackers can receive a version that allows them to manage the tool through their own domains.
According to Mushtaq, Hupigon's core function is to provide an attacker with backdoor access to the infected PC.
"After that, what the criminal does is only limited by his imagination," he said, noting the malware uses homegrown encryption to hide its command and control (CnC) communication. "The CnC servers are currently being operated from China."
The IE vulnerability at the center of all this is an invalid flag reference that can be exploited to permit remote code execution. Under certain conditions, it is possible for the invalid flag reference to be accessed after an object is deleted. In a specially crafted attack, in attempting to access a freed object, Internet Explorer can be caused to allow remote code execution, Microsoft stated in its advisory.
The vulnerability affects all supported versions of the browser-IE 6, 7 and 8. Microsoft listed a number of workarounds in the advisory, including configuring Internet and local intranet security zone settings to "high."
"I wasn't surprised that the IE zero-day has been incorporated into specific malware, namely Pirpi and Hupigon," Mushtaq said. "After the public disclosure of the vulnerability, other people created and refined proof of concept code making it work for IE 7.0. ...We can safely say this is just the first kit of several to begin incorporating this vulnerability attack vector."