An issue was discovered on COROS PACE 3 devices through 3.0808.0. It implements a function to connect the watch to a WLAN. This function is mainly for downloading firmware files. Before downloading firmware files, the watch requests some information about the firmware via HTTPS from the back-end API. However, the X.509 server certificate within the TLS handshake is not validated by the device. This allows an attacker within an active machine-in-the-middle position, using a TLS proxy and a self-signed certificate, to eavesdrop and manipulate the HTTPS communication. This could be abused, for example, for stealing the API access token of the assigned user account.