Dangerous 'RIPlace' Exploit Able to Bypass AV & EDR Protections

Security researchers Daniel Prizmant, Guy Meoded, Freddy Ouzan and Hanan Natan, who work at endpoint protection firm Nyotron, have found a way that ransomware can bypass the protections which operating system vendors have built into their products. Other software products that try and stop ransomware are also affected by the exploit.

Nyotron says that, "all antivirus products we have tested to date were bypassed. Even Endpoint Detection and Response (EDR) products that are supposed to keep track of all data-related activity are completely blind to this technique."

Calling it RIPlace, it can be implemented in only a few lines of code. It leverages a Windows operating system design flaw rather than a flaw in specific piece of software.

The exploit focuses on the step of ransomware where the original files are rewritten to an encrypted form and the original is destroyed. If the way this happens involves the Rename function, RIPlace is possible.

There is some work that needs to be done of course. If prior to calling Rename, DefineDosDevice is called (a legacy function that creates a symlink), an arbitrary name can be set as the device name. The original file path will then be the target to which it points. This way we can get our device "XY" to refer to "C:\passwords.txt". Nytron summarizes the crux of RIPlace as, "The RIPlace discovery is that in the callback function filter driver fails to parse the destination path when using the common routine FltGetDestinationFileNameInformation. It returns an error when passing a DosDevice path (instead of returning the path, post-processed); however, the Rename call succeeds."

So, the ransomware protection's MiniFilter driver sees an error, and therefore nothing is blocked. Yet, the Rename still succeeds and can change the file even if it has been encrypted.

While Neutron says that the technique "has not been detected in the wild (at least as far as we know), we have already alerted Microsoft and security vendors."

They also released a software tool (https://www.nyotron.com/riplace) to check if you are susceptible to this problem. It encrypts a file with XOR methods and tries to get it to show up in violation of Window's Controlled Folder Access (CFA) tool.

When another publication asked MSFT about all of this, they responded that that the technique is not considered a vulnerability and as CFA is a defense-in-depth feature, it does not satisfy their security servicing criteria. In short, they are ignoring it.

However, Kaspersky and Carbon Black have both reportedly modified their software in order to prevent RIPlace from being effective.

— Larry Loeb has written for many of the last century's major "dead tree" computer magazines, having been, among other things, a consulting editor for BYTE magazine and senior editor for the launch of WebWeek.