dyndnsupdate is a dyndns.org data updater written by Fredrik "xzabite" Haglund.
Toby Dickenson discovered that dyndnsupdate suffers from multiple overflows.
A remote attacker, posing as a dyndns.org server, could execute arbitrary code with the rights of the user running dyndnsupdate.
There is no known workaround at this time.
Currently, there is no released version of dyndnsupdate that contains a fix for these issues. The original xzabite.org distribution site is dead, the code contains several other problems and more secure alternatives exist, such as the net-dns/ddclient package. Therefore, the dyndnsupdate package has been hard-masked prior to complete removal from Portage, and current users are advised to unmerge the package:
# emerge --unmerge net-misc/dyndnsupdate