Gentoo Portage contains a flaw that may allow a malicious user to to overwrite arbitrary file reguardless of permissions. The issue is triggered when "dispatch-conf" script does not check permissions before writing to files in the /tmp directory occurs. It is possible that the flaw may allow overwrite a file that has root privilages resulting in a loss of integrity.
Upgrade to version 2.0.51-r3 or higher, as it has been reported to fix this vulnerability. An upgrade is required as there are no known workarounds.