The selinux_ptrace logic in hooks.c in SELinux for Linux 2.6.6 allows local users with ptrace permissions to change the tracer SID to an SID of another process.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A10102
http://www.securityfocus.com/bid/17830
http://www.redhat.com/support/errata/RHSA-2006-0575.html
http://www.mandriva.com/security/advisories?name=MDKSA-2006:086
http://www.debian.org/security/2006/dsa-1184
http://support.avaya.com/elmodocs2/security/ASA-2006-200.htm
http://selinuxnews.org/wp/index.php/2006/03/13/security-ptrace-bug-cve-2006-1052/
http://secunia.com/advisories/22417
http://secunia.com/advisories/22093
http://secunia.com/advisories/21465
http://secunia.com/advisories/20157
http://secunia.com/advisories/19955