The NE2000 emulator in QEMU 0.8.2 allows local users to execute arbitrary code by writing Ethernet frames with a size larger than the MTU to the EN0_TCNT register, which triggers a heap-based buffer overflow in the slirp library, aka NE2000 "mtu" heap overflow.  NOTE: some sources have used CVE-2007-1321 to refer to this issue as part of "NE2000 network driver and the socket code," but this is the correct identifier for the mtu overflow vulnerability.