Qpopper is a widely used server for the POP3 protocol.
Jens Steube discovered that Qpopper doesn't drop privileges to process local files from normal users (CAN-2005-1151). The upstream developers discovered that Qpopper can be forced to create group or world writeable files (CAN-2005-1152).
A malicious local attacker could exploit Qpopper to overwrite arbitrary files as root or create new files which are group or world writeable.
There is no known workaround at this time.
All Qpopper users should upgrade to the latest available version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=net-mail/qpopper-4.0.5-r3"