mpg123 is a real-time MPEG audio player.
mpg123 improperly parses frame headers in input streams.
By inducing a user to play a malicious file, an attacker may be able to exploit a buffer overflow to execute arbitrary code with the permissions of the user running mpg123.
There is no known workaround at this time.
All mpg123 users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=media-sound/mpg123-0.59s-r9"