Recent changes made to the Terror exploit kit (EK) allow it to fingerprint victims and target specific vulnerabilities instead of carpet bombing the victims with many exploits at the same time, Talos researchers discovered.
Terror was initially detailed in January this year, when security researchers observed that it was targeting vulnerabilities with exploits taken from Metasploit or from either Sundown or Hunter EKs. Terror activity increased last month, after the Sundown EK inexplicably disappeared from the threat landscape.
Previously, the EK was observed carpet bombing victims with many exploits at the same time, even if those exploits didn’t match the targeted browser environment. Now, the threat has added more exploits and is fingerprinting victim’s system to determine what exploit would be successful based on operating system, patch level, browser version, and installed plugins.
The use of more targeted exploits makes it more difficult for investigators to determine which exploits the toolkit has. However, “it is interesting to note that the adversaries are using an URL parameter in cleartext for the vulnerability they are going to exploit,” Talos says.
Additionally, Talos researchers identified a potentially compromised legitimate web site that appears to be operating as a malware gate. Initially redirecting visitors to a RIG landing page, the gate switched to Terror after a single day.
The compromised website redirects users to the EK landing page by using a HTTP 302 Moved Temporarily response. The page uses obfuscated Javascript code to evaluate the victim’s browser environment, then uses the return value of this function to submit a hidden form called ‘frm’.
More proof that the EK has moved away from its carpet bombing approach is the manner in which it selects exploits when attempting to infect the victim. The researchers were served different files when accessing the site via Internet Explorer 11 than when using Internet Explorer 8.
The EK also uses cookie-based authentication for downloading the exploits, which prevents third-parties from accessing them, the security researchers discovered. This approach prevents not only investigators from learning where from or how the victims were infected, but also stops competitors from stealing the exploits.
“We have seen that the exploit kit market is experiencing an ongoing change. Big players in this market disappear while new ones show up. The new players are fighting for customers by constantly improving their quality and techniques. They modify these techniques on an ongoing basis to improve their capability to bypass security tools. This clearly shows how important it is to make sure that all your systems are up to date,” Talos concludes.
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