SmarterTools SmarterMail less than build 6985 - .NET Deserialization Remote Code Execution

Description

This module exploits a vulnerability in the SmarterTools SmarterMail software for version numbers <= 16.x or for build numbers < 6985. The vulnerable versions and builds expose three .NET remoting endpoints on port 17001, namely /Servers, /Mail and /Spool. For example, a typical installation of SmarterMail Build 6970 will have the /Servers endpoint exposed to the public at tcp://0.0.0.0:17001/Servers, where serialized .NET commands can be sent through a TCP socket connection.

The three endpoints perform deserialization of untrusted data (CVE-2019-7214), allowing an attacker to send arbitrary commands to be deserialized and executed. This module exploits this vulnerability to perform .NET deserialization attacks, allowing remote code execution for any unauthenticated user under the context of the SYSTEM account. Successful exploitation results in full administrative control of the target server under the NT AUTHORITY\SYSTEM account.

This vulnerability was patched in Build 6985, where the 17001 port is no longer publicly accessible, although it can be accessible locally at 127.0.0.1:17001. Hence, this would still allow for a privilege escalation vector if the server is compromised as a low-privileged user.