Buffer overflow in the ccid_card_vscard_handle_message function in hw/ccid-card-passthru.c in QEMU before 0.15.2 and 1.x before 1.0-rc4 allows remote attackers to cause a denial of service (crash) and possibly execute arbitrary code via a crafted VSC_ATR message.

The pciej_write function in hw/acpi_piix4.c in the PIIX4 Power Management emulation in qemu-kvm does not check if a device is hotpluggable before unplugging the PCI-ISA bridge, which allows privileged guest users to cause a denial of service (guest crash) and possibly execute arbitrary code by sending a crafted value to the 0xae08 (PCI_EJ_BASE) I/O port, which leads to a use-after-free related to "active qemu timers."

The change_process_uid function in os-posix.c in Qemu 0.14.0 and earlier does not properly drop group privileges when the -runas option is used, which allows local guest users to access restricted files on the host.