Regarding CVE-2021-31251, it explains about the CHIYU serial converts & SEMAC door control panel has a security issue.
Because the telnet is able to connect with the device.

For this reason, CHIYU would like to include below the measures to fix the problem.

From now, all of the shipment has the latest firmware. The firmware will close telnet.

if you want to upgrade your converter's firmware, please contact CHIYU for upgrading. Contact:

I agree