Researchers at Symantec have detected a new variant of the Tidserv (TDL) malware that takes advantage of the Chromium Embedded Framework (CEF) to enhance its attack.
CEF is an open-source framework for embedding a Web browser control based on Google Chrome. This enables developers to create applications that have Web browser windows.
According to Symantec, the TDL malware is abusing CEF to move some basic Web browser functionality out of its own modules and into the CEF library.
"This allows for smaller modules that are easier to update with new functionality," Kevin Savage, a Symantec researcher, explained in a blog post. "The downside of Tidserv using CEF is that the cef32 module needs the CEF cef.dll Dynamic Link Library in order to load. The URL to the CEF Zip file for download is currently hardcoded in the serf332 binary, so any change to this URL will require an update to the serf332 module."
In the past, variants of Tidserv had used the serf332 module to perform network operations like link clicking and ad pop-ups using Component Object Model (COM) objects to open Web pages and inspect page content, Savage noted. Recently, Symantec observed Tidserv downloading a new module called cef32, which has the same functionality as serf332 but requires cef.dll, which is part of the CEF. This requires a download of the full 50MB CEF to the compromised system, he explained.
In response to the revelations, CEF developers posted a notice on the Website stating that they were aware that a CEF binary release file hosted on the CEF project page was being directly downloaded by a distributed malware product for "illegal purposes."
"The [CEF] project and its authors do not condone or promote the use of the CEF framework for illegal or illicit purposes," the notice said. "We will take all actions reasonably within our power to frustrate this use case. For that reason, current and future downloads will be hosted externally at http://www.magpcss.net/cef_downloads/. This new download location offers improved features and protections over those offered by Google Code hosting. We apologize for any inconvenience that this may cause our users who download CEF for legitimate purposes."
Satnam Narang, security response manager at Symantec, said this is the first time it has observed the CEF being used by malware.
"As a requirement for the threat to function correctly, it's noteworthy that the threat is instructed to download the 50MB framework, which is unusual," Narang told eWEEK.
The use of CEF indicates that "the threat is offloading some of the Web browser functionality to the CEF library to make its own modules leaner and thus easier to update in the future with new functionality," Narang added.
"There has been a considerable increase in the download of the CEF over the last 18 days," Savage blogged. "While we cannot be certain as to how many of these downloads may relate to Tidserv infection activities, if these downloads are a result of the malware, the number of computers compromised [by] Tidserv would be sizable."