glibc is a package that contains the GNU C library.
The catchsegv script creates temporary files in world-writeable directories with predictable names.
A local attacker could create symbolic links in the temporary files directory, pointing to a valid file somewhere on the filesystem. When catchsegv script is called, this would result in the file being overwritten with the rights of the user running the utility, which could be the root user.
There is no known workaround at this time.
All glibc users should upgrade to the latest version:
# emerge sync
# emerge -pv sys-libs/glibc
# emerge sys-libs/glibc