In PuTTY versions before 0.71 on Unix, a remotely triggerable buffer overflow exists in any kind of server-to-client forwarding.
https://www.debian.org/security/2019/dsa-4423
https://www.chiark.greenend.org.uk/~sgtatham/putty/changes.html
https://security.netapp.com/advisory/ntap-20190404-0001/
https://seclists.org/bugtraq/2019/Apr/6
http://lists.opensuse.org/opensuse-security-announce/2019-04/msg00020.html
http://lists.opensuse.org/opensuse-security-announce/2019-04/msg00004.html