An Iran-linked group called OilRig has been conducting cyber espionage since at least 2015. Its latest escapade involves the Internet Information Services (IIS) servers that have been used by other Middle Eastern government organizations, as well as financial and educational institutions.
What the group does with the IIS servers is to put a backdoor on them called the TwoFace webshell. This shell will in turn enable the Mimikatz tool, which is used to snarf up the login credentials of users. Having those available, OilRig can get to anything on the server.
The shell is multilayered, and able to live in the server undetected and functional for long periods of time. This gives it a big strategic advantage over other methods of compromise. The longer it can be active, the more credentials it can send back to its creator.
Additionally, the TwoFace webshell can spread laterally, replicating itself on other connected web servers which can then be compromised.
TwoFace installs a secondary backdoor on top of itself, called RGDoor. It can allow OilRig to re-compromise the affected server if the TwoFace shell is discovered and mediated.
RGDoor seems to have been created in C++, ending up as a compiled dynamic link library (DLL).
IIS has a feature where DLLs can extend its capabilities to help carry out custom actions on requests. This is the manner that RGDoor acts.
"This backdoor has a rather limited set of commands, however, the three commands ['cmd$,' 'upload$' and 'download$' -- ed.] provide plenty of functionality for a competent backdoor, as they allow an actor to upload and download files to the sever, as well as run commands via command prompt," according to Palo Alto.
This kind of detailed planning about a target shows the seriousness of OilRig's threat.
Once the group gets hold of the server, even if the primary malware is nullified, OilRig has a backup plan in place to continue its campaign. The backdoor within the backdoor is both functional and works by other methods than the primary backdoor does.
This kind of campaign shows the sophistication and stealth techniques that nation-states will use to obtain their goals. They do not make the same kinds of errors that an adversary, which has limited financial goals, will make.
An attack launched by this kind of threat actor requires defenders to consider the kinds of alternatives that may not be necessary in simple breaches.
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— 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.