The Mach kernel, as used in operating systems including (1) Mac OS X 10.4 through 10.4.7 and (2) OpenStep before 4.2, allows local users to gain privileges via a parent process that forces an exception in a setuid child and uses Mach exception ports to modify the child's thread context and task address space in a way that causes the child to call a parent-controlled function.
Buffer overflow in lpr, as used in BSD-based systems including Linux, allows local users to execute arbitrary code as root via a long -C (classification) command line option.
rdist in various UNIX systems uses popen to execute sendmail, which allows local users to gain root privileges by modifying the IFS (Internal Field Separator) variable.
Vulnerability in NeXT 1.0a and 1.0 with publicly accessible printers allows local users to gain privileges via a combination of the npd program and weak directory permissions.