arch/x86/kernel/ptrace.c in the Linux kernel before 2.6.25.10 on the x86_64 platform leaks task_struct references into the sys32_ptrace function, which allows local users to cause a denial of service (system crash) or have unspecified other impact via unknown vectors, possibly a use-after-free vulnerability.
git.kernel.org/?p=linux/kernel/git/stable/linux-2.6.25.y.git%3Ba=commitdiff%3Bh=1e9a615bfce7996ea4d815d45d364b47ac6a74e8
kernel.org/pub/linux/kernel/v2.6/ChangeLog-2.6.25.10
secunia.com/advisories/31048
www.openwall.com/lists/oss-security/2008/07/03/2
www.securityfocus.com/bid/30077
www.vupen.com/english/advisories/2008/2063/references