An integer overflow was found in QEMU 4.0.1 through 4.2.0 in the way it implemented ATI VGA emulation. This flaw occurs in the ati_2d_blt() routine in hw/display/ati-2d.c while handling MMIO write operations through the ati_mm_write() callback. A malicious guest could abuse this flaw to crash the QEMU process, resulting in a denial of service.
https://usn.ubuntu.com/4372-1/
https://git.qemu.org/?p=qemu.git%3Ba=commit%3Bh=ac2071c3791b67fc7af78b8ceb320c01ca1b5df7