MirBSD Korn Shell is an actively developed free implementation of the Korn Shell programming language and a successor to the Public Domain Korn Shell.
Improper sanitation of environment import allows for appending of values to passed parameters.
An attacker who already had access to the environment could so append values to parameters passed through programs (including sudo(8) or setuid) to shell scripts, including indirectly, after those programs intended to sanitise the environment, e.g. invalidating the last $PATH component.
There is no known workaround at this time.
All mksh users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=app-shells/mksh-50c"