A man-in-the-middle (MITM) attack happens when an attacker positions themselves between two communicating endpoints and intercepts, relays, or changes traffic without either side realizing it. The attacker may read data, steal credentials, inject commands, or replace files and updates in transit. MITM is dangerous because the endpoints still appear to be talking to each other, so the compromise can look like a normal connection unless strong verification is in place.
In cyber security, MITM attacks often succeed when certificate validation, integrity checks, or network trust rules are weak. On a router or other edge device, that can let a spoofed server impersonate a legitimate update source and push attacker-controlled content or commands. Defenses include encrypted channels, strict certificate checking, integrity verification, secure DNS, and avoiding insecure management paths. The key lesson is simple: if a device cannot reliably confirm who it is talking to, a network-positioned attacker may be able to control what it receives.