eix is a small utility for searching ebuilds with indexing for fast results.
Eric Romang discovered that eix creates a temporary file with a predictable name. eix creates a temporary file in /tmp/eix.*.sync where * is the process ID of the shell running eix.
A local attacker can watch the process list and determine the process ID of the shell running eix while the "emerge --sync" command is running, then create a link from the corresponding temporary file to a system file, which would result in the file being overwritten with the rights of the user running the application.
There is no known workaround at this time.
All eix users should upgrade to the latest version:
# emerge --sync # emerge --ask --oneshot --verbose app-portage/eix