libvorbis is the reference implementation of the Xiph.org Ogg Vorbis audio file format. It is used by many applications for playback of Ogg Vorbis files.
Will Drewry of the Google Security Team reported multiple vulnerabilities in libvorbis:
A remote attacker could exploit these vulnerabilities by enticing a user to open a specially crafted Ogg Vorbis file or network stream with an application using libvorbis. This might lead to the execution of arbitrary code with the privileges of the user playing the file or a Denial of Service by a crash or CPU consumption.
There is no known workaround at this time.
All libvorbis users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=media-libs/libvorbis-1.2.1_rc1"