11/18/2023 0 Comments Winfo cifsIn this capture, we can see that the rpcclient goes through four stages before finally reaching an error condition. Let’s now look at the rpcclient connection: The first few RPC calls extracted information regarding the system’s local domain, while QueryDisplayInfo used that information to produce a list of all users within that domain. It then opens up the samr named pipe, and runs several RPC calls, including Connect4, EnumDomains, LookupDomain,OpenDomain and QueryDisplayInfo, each of which completes successfully. It firsts establishes an anonymous session with the SMB server and then accesses the IPC$ share. The smb-enum-users script goes through various phases, as highlighted by the different boxes. To understand why this behaviour occurs, let’s look at the Wireshark trace of each connection starting with the capture of smb-enum-users which was able to enumerate a list of users on the system: However, when I used rpcclient to execute the QueryDisplayInfo RPC call, it failed to enumerate the user information and instead produced the following output: Under the hood, the smb-enum-users’ script executes the QueryDisplayInfo RPC call to enumerate user information. In these tests, I ran rpcclient and nmap’s smb-enum-users NSE script against the same vulnerable system and viewed the output.īelow, the output of the smb-enum-users script shows that it was possible to enumerate the user information: In a penetration test scenario, this behaviour could make one believe that the remote system does not allow one to access the IPC$ share and execute RPC calls, while it could be possible. Another is Nmap’s smb-enum-user NSE script.ĭuring some tests, I found that when I used rpcclient against known vulnerable systems, that it would often produce error messages and fail to enumerate user information. There are numerous guides on how to disable NULL sessions, with some somewhat confusing advice from Microsoft’s side regarding what setting does what exactly.Īn application that has grown in popularity to test for NULL sessions is rpcclient, which other tools like enum4linux and ridenum uses under their hoods. From Windows XP onwards one can disable NULL sessions, or it is disabled by default. After applications like Cain& Able and others allowed one to exploit it, Microsoft clamped down on it. I remember learning about it in “Hacking For Dummies” in 2004, and by then it was already well known. Arguably the most useful information one could extract in this manner is user and group listings, which can be used in brute force attacks. Such a connection is often referred to as a NULL session, which while limited in its privileges, could be used to execute various RPC calls and as a result obtain useful information about the remote system. One can use such named pipes to execute specific functions, often referred to as Remote Procedure Calls (RPC) on the remote system.Ĭertain versions of Windows allowed one to authenticate and mount the IPC$ share without providing a username or password. Any data written to such a named pipe is sent to the remote process, and conversely any output data written by the remote process can be read by a local application from the pipe. Such named pipes are created when an application opens a pipe and registers it with the Windows Server service (SMB), such that it can be exposed by the IPC$ share. Specifically, IPC$ exposes named pipes, that one can write to or read from to communicate with remote processes. That is, it doesn’t allow one to access files or directories like other shares, but rather allows one to communicate with processes running on the remote system. IPC$ is a special share that is used to facilitate inter-process communication (IPC). To be able to mount these shares however, one needs to be an administrator on the remote system. Another share, Admin$, allows one to access the Windows installation directory. For example, C$ will allow one to access the C Drive. Some of these shares allow one to access the complete storage device on remote systems. Over the years, I have often used the NULL session vulnerability to enumerate lists of users, groups, shares and other interesting information from remote Windows systems.įor the uninitiated, Windows exposes several administrative and hidden shares via SMB by default. TLDR I think I found three new ways to do user enumeration on Windows domain controllers, and I wrote some scripts for it.
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