utility.c in telnetd in netkit telnet through 0.17 allows remote attackers to execute arbitrary code via short writes or urgent data, because of a buffer overflow involving the netclear and nextitem functions.
https://www.oracle.com/security-alerts/cpuApr2021.html
https://www.arista.com/en/support/advisories-notices/security-advisories/10702-security-advisory-48
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-telnetd-EFJrEzPx
https://lists.debian.org/debian-lts-announce/2020/08/msg00038.html
https://lists.debian.org/debian-lts-announce/2020/05/msg00012.html
https://appgateresearch.blogspot.com/2020/02/bravestarr-fedora-31-netkit-telnetd_28.html