xpvm.tcl in xpvm 1.2.5 allows local users to overwrite arbitrary files via a symlink attack on the xpvm.trace.$user temporary file.
http://www.zataz.net/adviso/xpvm-06272005.txt
http://www.securityfocus.com/bid/14228
http://www.debian.org/security/2006/dsa-1003