ldd in the GNU C Library (aka glibc or libc6) 2.13 and earlier allows local users to gain privileges via a Trojan horse executable file linked with a modified loader that omits certain LD_TRACE_LOADED_OBJECTS checks. NOTE: the GNU C Library vendor states "This is just nonsense. There are a gazillion other ways to introduce code if people are downloading arbitrary binaries and install them in appropriate directories or set LD_LIBRARY_PATH etc.