Cleartext traffic is network data sent without encryption. In mobile and IoT apps, that can include device status, authentication tokens, telemetry, or control commands. Anyone on the path—such as a Wi-Fi attacker, proxy, or compromised router—can read it, and in some cases alter it before it reaches the destination.
This matters because plaintext transport turns ordinary communication into an easy interception target. Attackers can sniff credentials, replay requests, or inject malicious responses. Defenders reduce the risk by requiring HTTPS/TLS, validating certificates, and disabling plaintext fallbacks in app or platform settings. In code reviews and penetration tests, cleartext traffic often shows up as HTTP endpoints, raw socket usage, or legacy libraries that never got updated. In abandoned companion apps, it can remain a live exposure long after the product is unsupported.