Qemu emulator <= 3.0.0 built with the NE2000 NIC emulation support is vulnerable to an integer overflow, which could lead to buffer overflow issue. It could occur when receiving packets over the network. A user inside guest could use this flaw to crash the Qemu process resulting in DoS.
https://www.openwall.com/lists/oss-security/2018/10/08/1
https://www.debian.org/security/2018/dsa-4338
https://usn.ubuntu.com/3826-1/
https://lists.gnu.org/archive/html/qemu-devel/2018-09/msg03273.html
https://lists.debian.org/debian-lts-announce/2018/11/msg00038.html