Dropbear is an SSH server and client with a small memory footprint.
Under certain conditions Dropbear could fail to allocate a sufficient amount of memory, possibly resulting in a buffer overflow.
By sending specially crafted data to the server, authenticated users could exploit this vulnerability to execute arbitrary code with the permissions of the SSH server user, which is the root user by default.
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-0.47"