The fn_show_postinst function in Gentoo webapp-config before 1.10-r14 allows local users to overwrite arbitrary files via a symlink attack on the postinst.txt temporary file.
http://www.vupen.com/english/advisories/2005/0809
http://www.securityfocus.com/bid/13780
http://www.gentoo.org/security/en/glsa/glsa-200506-13.xml