QEMU (aka Quick Emulator) built with the USB EHCI emulation support is vulnerable to a null pointer dereference flaw. It could occur when an application attempts to write to EHCI capabilities registers. A privileged user inside quest could use this flaw to crash the QEMU process instance resulting in DoS.
https://security.gentoo.org/glsa/201604-01
https://lists.gnu.org/archive/html/qemu-devel/2016-01/msg05899.html
https://lists.debian.org/debian-lts-announce/2018/09/msg00007.html
https://bugzilla.redhat.com/show_bug.cgi?id=1301643