ptrace in Linux 2.2.x through 2.2.19, and 2.4.x through 2.4.9, allows local users to gain root privileges by running ptrace on a setuid or setgid program that itself calls an unprivileged program, such as newgrp.
http://www.securityfocus.com/bid/3447
http://www.redhat.com/support/errata/RHSA-2001-130.html
http://www.redhat.com/support/errata/RHSA-2001-129.html
http://www.novell.com/linux/security/advisories/2001_036_kernel_txt.html
http://www.linuxsecurity.com/advisories/other_advisory-1650.html
http://www.linux-mandrake.com/en/security/2001/MDKSA-2001-082.php3
http://www.linux-mandrake.com/en/security/2001/MDKSA-2001-079.php3
http://www.iss.net/security_center/static/7311.php
http://online.securityfocus.com/advisories/3713
http://marc.info/?l=bugtraq&m=100350685431610&w=2
http://marc.info/?l=bugtraq&m=100343090106914&w=2
http://download.immunix.org/ImmunixOS/7.0/updates/IMNX-2001-70-035-01