A telnet bugfix update has been released for CentOS 7.

CentOS-announce: CEBA-2020:5019 CentOS 7 telnet BugFix Update

CentOS Errata and Bugfix Advisory 2020:5019

Upstream details at :   https://access.redhat.com/errata/RHBA-2020:5019

The following updated files have been uploaded and are currently
syncing to the mirrors: ( sha256sum Filename )

x86_64:
100f1234d4c5782b5913aa69ba66a3d90098ad06808fb39b4433d80beb94075d telnet-0.17-66.el7.x86_64.rpm
94d47b782d9d01f589874cfe848688d584d291d216cca5e37b467e4d747dd75e telnet-server-0.17-66.el7.x86_64.rpm

Source:
7155b1337b9620c9a2a8b38738395d5afdeb6854e059162f67899f0f5e5871c8 telnet-0.17-66.el7.src.rpm