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 ati2dblt() routine in hw/display/ati-2d.c while handling MMIO write operations through the atimmwrite() callback. A malicious guest could abuse this flaw to crash the QEMU process, resulting in a denial of service.