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Unfortunately, the DCERPC protocol’s multiplexed nature makes it more difficult to analyze than other protocols. In the case of DCERPC, this state information is stored in c$dce_rpc, c$dce_rpc_state, and c$dce_rpc_backing.
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Also like the SMB sessions, Zeek stores state information about the current DCERPC call or response in several places within the c variable. Again, Zeek takes care of most of these details for us by treating DCERPC as just another network layer above SMB. The next step in detecting a PetitPotam exploit is to dissect the DCERPC function calls that ride on top of the SMB session, and look for signs of someone attempting to trigger an NTLM relay by making an EFS function call.
#AVAST SANDBOXING TOR RELAY KASEYA AGENT UPDATE#
As each SMB session progresses, Zeek will add or update values to this subrecord so that it represents a summary of the SMB session’s current state. What you need to know is that Zeek is tracking this type of information for us across the lifetime of each SMB session. Figure 1 shows a small portion of the information that Zeek has recorded about an SMB read operation from \\192.168.0.85\IPC$ (Note: this snippet is paired down for readability there is a lot more information available in c$smb_state). For example, additional information about the current state of each SMB session is stored in c$smb_state. By tradition, the connection record is referred to by the variable c, and additional information about each connection is stored in sub-variables delimited by the $ operator.
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This information is stored inside of the record that Zeek keeps for each network connection that it sees. Zeek takes care of tracking the state of each SMB session and its associated TCP session for us out of the box by storing much of what it knows for later use. In most cases, calling a remote DCERPC function occurs over an SMB session, so each exploitation starts by negotiating the SMB session’s parameters.
#AVAST SANDBOXING TOR RELAY KASEYA AGENT WINDOWS#
PetitPotam exploitation works by abusing the lack of sufficient permission checking when calling EFS DCERPC functions on remote Windows systems. There is no single packet or portion of the ongoing conversation that contains everything necessary for detection.įirst, let’s examine the different parts of a successful PetitPotam exploitation, and then we’ll see how Zeek tracks the state of the network protocols for us to enable the detection process. As a result, detecting this exploit requires tracking the state of several network protocols over the lifetime of their sessions. The exploit takes place inside of an SMB session that involves several phases that must be tracked: the negotiation of the session’s parameters, an authentication, one or more RPC function calls, and their matching responses. PetitPotam abuses EFS DCERPC functions to trigger an NTLM relay attack that can be used to gain elevated privileges in a Windows AD domain. The PetitPotam exploit offers an opportunity to illustrate the power of Zeek for tracking the state of network conversations over their lifetime. We will walk through how this works in this blog post. To illustrate this point, here is a Zeek script for detecting attempts to exercise the PetitPotam exploits. This is particularly useful when examining network protocols such as Server Message Block (SMB) that rely on the endpoint devices to track the state of their conversation. There is another strength that is often overlooked: Zeek not only extracts information from individual packets of network sessions, it also provides a very flexible and useful way to track state across the lifetime of network sessions. It is adept not only at identifying network protocols but also parsing them to extract large amounts of useful information. One of Zeek's greatest strengths is its ability to deeply inspect packet streams that are fed into it.