The LinuxCIFS utils are a collection of tools for managing Linux CIFS Client Filesystems.
The mount.cifs utility had a shell injection issue where one can embed shell commands via the username mount option. Those commands will be run via popen() in the context of the user calling mount.
A remote attacker could entice a user to use a specially crafted argument using mount.cifs, possibly resulting in execution of arbitrary code with the privileges of the process or a Denial of Service condition.
There is no known workaround at this time.
All LinuxCIFS users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=net-fs/cifs-utils-6.11"