scponly is a restricted shell, allowing only a few predefined commands. It is often used as a complement to OpenSSH to provide access to remote users without providing any remote execution privileges.
Max Vozeler discovered that the scponlyc command allows users to chroot into arbitrary directories. Furthermore, Pekka Pessi reported that scponly insufficiently validates command-line parameters to a scp or rsync command.
A local attacker could gain root privileges by chrooting into arbitrary directories containing hardlinks to setuid programs. A remote scponly user could also send malicious parameters to a scp or rsync command that would allow to escape the shell restrictions and execute arbitrary programs.
There is no known workaround at this time.
All scponly users should upgrade to the latest version:
# emerge --sync # emerge --ask --oneshot --verbose ">=net-misc/scponly-4.2"