Heartbeat is a component of the High-Availability Linux project. It it used to perform death-of-node detection, communications and cluster management.
Eric Romang has discovered that Heartbeat insecurely creates temporary files with predictable filenames.
A local attacker could create symbolic links in the temporary file directory, pointing to a valid file somewhere on the filesystem. When a vulnerable script is executed, this could lead to the file being overwritten with the rights of the user running the affected application.
There is no known workaround at this time.
All Heartbeat users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=sys-cluster/heartbeat-1.2.3-r1"