The Tar program provides the ability to create and manipulate tar archives.
The sparse_dump_region function in sparse.c file in Tar allows an infinite loop using the --sparse option.
A local attacker could cause a Denial of Service condition by modifying a file that is supposed to be archived by a different user’s process (e.g., a system backup running as root).
There is no known workaround at this time.
All Tar users should upgrade to the latest version:
# emerge --sync # emerge --ask --oneshot --verbose ">=app-arch/tar-1.30-r1"