Dropbear is a relatively small SSH server and client.
A CRLF injection vulnerability in Dropbear SSH allows remote authenticated users to bypass intended shell-command restrictions via crafted X11 forwarding data.
A remote authenticated user could execute arbitrary code with the privileges of the process.
There is no known workaround at this time.
All Dropbear users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=net-misc/dropbear-2016.73"