Adversaries with privileged network access may seek to modify network traffic in real time using man-in-the-middle (MITM) attacks.  This type of attack allows the adversary to intercept traffic to and/or from a particular device on the network. If a MITM attack is established, then the adversary has the ability to block, log, modify, or inject traffic into the communication stream. There are several ways to accomplish this attack, but some of the most-common are Address Resolution Protocol (ARP) poisoning and the use of a proxy. 
The VPNFilter's ssler module configures the device's iptables to redirect all traffic destined for port 80 to its local service listening on port 8888. Any outgoing web requests on port 80 are now intercepted by ssler and can be inspected by the ps module and manipulated before being sent to the legitimate HTTP service.  
Limit access to network infrastructure and resources that can be used to reshape traffic or otherwise produce MiTM conditions.
Communication authenticity will ensure that any messages tampered with through MITM can be detected, but cannot prevent eavesdropping on these. In addition, providing communication authenticity around various discovery protocols, such as DNS, can be used to prevent various MITM procedures.
|M0942||Disable or Remove Feature or Program||
Disable unnecessary legacy network protocols that may be used for MiTM if applicable.
|M0931||Network Intrusion Prevention||
Network intrusion detection and prevention systems that can identify traffic patterns indicative of MiTM activity can be used to mitigate activity at the network level.
Network segmentation can be used to isolate infrastructure components that do not require broad network access. This may mitigate, or at least alleviate, the scope of MiTM activity.
|M0810||Out-of-Band Communications Channel||
Utilize out-of-band communication to validate the integrity of data from the primary channel.
|M0813||Software Process and Device Authentication||
To protect against MITM, authentication mechanisms should not send credentials across the network in plaintext and should also implement mechanisms to prevent replay attacks (such as nonces or timestamps). Challenge-response based authentication techniques that do not directly send credentials over the network provide better protection from MITM.
|M0814||Static Network Configuration||
Statically defined ARP entries can prevent manipulation and sniffing of switched network traffic, as some MitM techniques depend on sending spoofed ARP messages to manipulate network host's dynamic ARP tables.
|ID||Data Source||Data Component|
|DS0029||Network Traffic||Network Traffic Content|
|Network Traffic Flow|
|DS0009||Process||OS API Execution|