TDL Malware Updated to Use Chromium Embedded Framework

Symantec says they have discovered a new variant of the TDL (Tidserv) family of malware that downloads the full legitimate Chromium Embedded Framework (CEF) as part of its normal operation.

While malware using legit development platforms isn’t unheard of, Symantec notes, the fact that the latest incarnation of TDL downloads the entire 50MB CEF core is a bit odd.

CEF is a framework for embedding controls in desktop applications, or add additional functionality to a given app. It’s useful for adding HTML 5 GUIs to desktop applications, and it’s handy for developers as it can be used with C, C++, Java, .NET, and Python – on Windows, Linux, or OS X.

The wide range of platform and code adoption within CEF is likely why the authors are using it for TDL, as the moneymaking rootkit could gain traction if it were to branch out from Windows to other operating systems. However, while the malware’s latest module-driven design has some unique code, the malware is useless unless the compromised host downloads the full framework – all 50MB of it.

“While this may not be the first time a malware has made use of a legitimate framework for nefarious purposes, this new [TDL] variant requires the download of the 50 MB framework to function correctly, which is an unusual thing for a threat to do,” Symantec said in a blog post.

While Symantec can’t say for certain if the spike in downloads for CEF is directly related to the latest TDL variant, they’re certain that some of them are malicious in nature. As of last Friday, there were more than 20,000 CEF downloads.

TDL is only using one aspect of the framework for its modular functions, and in order to prevent their code form being maliciously abused, the CEF project members have removed the needed library from access and are exploring alternative options of delivering cef.dll, which may include altering the serf332 module itself.

For the history of TDL, Symantec has a running tab on the malware family posted online for those who are curious.