The winbind plugin in pppd for ppp 2.4.4 and earlier does not check the return code from the setuid function call, which might allow local users to gain privileges by causing setuid to fail, such as exceeding PAM limits for the maximum number of user processes, which prevents the winbind NTLM authentication helper from dropping privileges.
http://www.ubuntu.com/usn/usn-310-1
http://www.securityfocus.com/bid/18849
http://www.mandriva.com/security/advisories?name=MDKSA-2006:119
http://www.debian.org/security/2006/dsa-1106
http://secunia.com/advisories/20996
http://secunia.com/advisories/20987