Unencrypted MS-EVEN6 Traffic

This blog entry is intended for readers interested in generating unencrypted MS-EVEN6 ( https://msdn.microsoft.com/en-us/library/cc231282(v=PROT.13).aspx ) protocol traffic.

NOTE: Questions and comments are welcome. However, please DO NOT post a comment using the comment tool at the end of this post. Instead, post a new thread in the Open Specifications Forum: Windows Protocols at https://social.msdn.microsoft.com/Forums/en-US/os_windowsprotocols .

Can windows inbox tools be configured to generate unencrypted traffic?

No, Windows inbox tools eventviewer and wevtutil generates encrypted MS-EVEN6 traffic and there is NO registry setting to alter this behavior. These tools invokes RPC bind with authentication-level set to RPC_C_AUTHN_LEVEL_PKT_PRIVACY which ensures encrypting the argument value of each remote procedure call. Refer below screenshot highlighting authentication-level field.

 What does MS-EVEN6 specification say about authentication-level?

MS-EVEN6 specification, https://msdn.microsoft.com/en-us/library/cc231303(v=prot.13), does not impose any such constraint on authentication-level and we confirmed that windows server does accept RPC bind with authentication-level set to RPC_C_AUTHN_LEVEL_PKT_INTEGRITY. Benefit of using RPC_C_AUTHN_LEVEL_PKT_INTEGRITY authentication-level over RPC_C_AUTHN_LEVEL_PKT_PRIVACY --- MS-EVEN6 traffic will be unencrypted.

This is a good news for the implementers interested in analyzing unencrypted EVEN6 packet. But it requires some work as we have to write a custom client with authentication-level set to RPC_C_AUTHN_LEVEL_PKT_INTEGRITY during RPC bind and then use that binding handle to invoke EVEN6 methods 

A feasible option to generate unencrypted MS-EVEN6 traffic

I recently wrote a sample application in C++ to generate unencrypted protocol traffic and detail steps are as follows:

1. Install visual studio 2008/2010 Ultimate/professional on a development machine.

2. Copy and paste the IDL given in EVEN6 [MS_EVEN6] specification to a notepad and save file as even6.idl

3. Since it’s an RPC based protocol, copy and paste IDL given in MS-RPCE specification to notepad and save file as ms-rpce.idl

4. Place both the above files in same folder and use MIDL compiler to generate stub and header files. For this, go to start, type “visual studio”, launch “Visual Studio Command Prompt” and issue below command:

midl even6.idl

5. Step 4 will generate even6.h, ms-rpce.h, even6_c.c which you need to include in your project. Choose VC++, Win32 console application as project type.

6. In the file that has “_tmain” function, include header files and create binding handle (IfHandle) that has to be passed to EVEN6 methods. Following snippet shows how to create a binding handle:

int bindStatus, bStatStringBnd;

RPC_BINDING_HANDLE IfHandle = NULL;

RPC_WSTR pszStringBinding;

TCHAR *pszEven6UUID = TEXT("F6BEAFF7-1E19-4FBB-9F8F-B89E2018337C");

TCHAR *pszEndpoint  = TEXT("");

TCHAR *protoSeq = TEXT("ncacn_ip_tcp");

wchar_t exceptionString[512];

ULONG_PTR lpArguments = (ULONG_PTR)exceptionString;

pszStringBinding = (RPC_WSTR)MIDL_user_allocate(512);

bindStatus = RpcStringBindingCompose( (RPC_WSTR)pszEven6UUID, (RPC_WSTR)protoSeq, (RPC_WSTR)pszServer, NULL, NULL, (RPC_WSTR*)&pszStringBinding);

if (RPC_S_OK == bindStatus){ printf ("The call succeeded. RpcStringBindingCompose\n");

}

if (RPC_S_INVALID_STRING_UUID == bindStatus) {  sprintf((char *)exceptionString, "The string representation of the UUID: , %s , is not valid.\n", pszEven6UUID);

RaiseException( bindStatus, 0, 1, &lpArguments );

}

bStatStringBnd = RpcBindingFromStringBinding( (RPC_WSTR)pszStringBinding, &IfHandle);

bStatStringBnd = RpcBindingSetAuthInfo( IfHandle, (RPC_WSTR)pszServer, RPC_C_AUTHN_LEVEL_PKT_INTEGRITY, RPC_C_AUTHN_WINNT, NULL, RPC_C_AUTHZ_NAME);

7. Pass this IfHandle to various EVEN6 calls, I tested EvtRpcOpenLogHandle, and you should be able to generate unencrypted traffic.

If (RPC_S_OK == bStatStringBnd) {

hEven6Binding = IfHandle;

RpcInfo error2;

error_status_t error = EvtRpcOpenLogHandle(L"Application", 1, (PCONTEXT_HANDLE_LOG_HANDLE*)&hEven6Binding, &error2);

}

Bind Request Packet with authentication-level as RPC_C_AUTHN_LEVEL_PKT_INTEGRITY:

 
 Bind Response Packet with authentication-level as RPC_C_AUTHN_LEVEL_PKT_INTEGRITY:

 
 Unencrypted EvtRpcOpenLogHandle request packet:

Unencrypted EvtRpcOpenLogHandle response packet:

References:

Open Specifications Support Team Blog: https://blogs.msdn.com/b/openspecification/

Open Specifications Forums: https://blogs.msdn.com/b/openspecification/

Open Specifications Forum/Windows Protocols: https://social.msdn.microsoft.com/Forums/en-US/os_windowsprotocols/threads

Network Monitor Blog: https://blogs.technet.com/b/netmon/