CUPS, the Common Unix Printing System, is a full-featured print server.
Members of the lpadmin group have admin access to the web interface, where they can edit the config file and set some “dangerous” directives (like the logfilenames), which enable them to read or write files as the user running the CUPS webserver.
A local attacker could possibly exploit this vulnerability to read or write files as the user running the CUPS webserver.
There is no known workaround at this time.
All CUPS users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=net-print/cups-1.6.2-r5"