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Category:   Application (Generic)  >   Red Hat Enterprise Virtualization Vendors:   Red Hat
(Red Hat Issues Fix for Red Hat Enterprise Virtualization) Xen Virtio Request Processing Bug Lets Local Administrative Users on a Guest System Cause Denial of Service Conditions on the Host System
SecurityTracker Alert ID:  1036621
SecurityTracker URL:
CVE Reference:   CVE-2016-5403   (Links to External Site)
Date:  Aug 15 2016
Impact:   Denial of service via network
Fix Available:  Yes  Vendor Confirmed:  Yes  

Description:   A vulnerability was reported in Xen. A local administrative user on the guest system can cause denial of service conditions on the host system. Red Hat Enterprise Virtualization is affected.

A local administrative user on the guest system can submit specially crafted virtio request to exceed the virtqueue limit and consume all available memory in QEMU to cause denial of service conditions on the host system.

HVM domains where virtio-net devices are provided to the guest system are affected.

ARM systems are not affected.

PV domains are not affected.

HVM domains running with QEMU stub domains are not affected.

Zhenhao Hong of the 360 Marvel Team reported this vulnerability.

Impact:   A local administrative user on the guest system can cause denial of service conditions on the host system.
Solution:   Red Hat has issued a fix for Red Hat Enterprise Virtualization.

The Red Hat advisory is available at:

Vendor URL: (Links to External Site)
Cause:   Resource error
Underlying OS:  Linux (Red Hat Enterprise)

Message History:   This archive entry is a follow-up to the message listed below.
Jul 29 2016 Xen Virtio Request Processing Bug Lets Local Administrative Users on a Guest System Cause Denial of Service Conditions on the Host System

 Source Message Contents

Subject:  [RHSA-2016:1607-01] Moderate: qemu-kvm-rhev security update

Hash: SHA1

                   Red Hat Security Advisory

Synopsis:          Moderate: qemu-kvm-rhev security update
Advisory ID:       RHSA-2016:1607-01
Product:           Red Hat Enterprise Virtualization
Advisory URL:
Issue date:        2016-08-12
CVE Names:         CVE-2016-5126 CVE-2016-5403 

1. Summary:

An update for qemu-kvm-rhev is now available for RHEV-H and Agents for

Red Hat Product Security has rated this update as having a security impact
of Moderate. A Common Vulnerability Scoring System (CVSS) base score, which
gives a detailed severity rating, is available for each vulnerability from
the CVE link(s) in the References section.

2. Relevant releases/architectures:

RHEV-H and VDSM for 7 Hosts - ppc64le, x86_64

3. Description:

KVM (Kernel-based Virtual Machine) is a full virtualization solution for
Linux on AMD64 and Intel 64 systems. The qemu-kvm-rhev package provides the
user-space component for running virtual machines using KVM in environments
managed by Red Hat Enterprise Virtualization Manager.

Security Fix(es):

* Quick Emulator(Qemu) built with the Block driver for iSCSI images support
(virtio-blk) is vulnerable to a heap buffer overflow issue. It could occur
while processing iSCSI asynchronous I/O ioctl(2) calls. A user inside guest
could use this flaw to crash the Qemu process resulting in DoS or
potentially leverage it to execute arbitrary code with privileges of the
Qemu process on the host. (CVE-2016-5126)

* Quick emulator(Qemu) built with the virtio framework is vulnerable to an
unbounded memory allocation issue. It was found that a malicious guest user
could submit more requests than the virtqueue size permits. Processing a
request allocates a VirtQueueElement and therefore causes unbounded memory
allocation on the host controlled by the guest. (CVE-2016-5403)

Red Hat would like to thank hongzhenhao (Marvel Team) for reporting

4. Solution:

For details on how to apply this update, which includes the changes
described in this advisory, refer to:

After installing this update, shut down all running virtual machines. Once
all virtual machines have shut down, start them again for this update to
take effect.

5. Bugs fixed (

1340924 - CVE-2016-5126 Qemu: block: iscsi: buffer overflow in iscsi_aio_ioctl
1358359 - CVE-2016-5403 Qemu: virtio: unbounded memory allocation on host via guest leading to DoS

6. Package List:

RHEV-H and VDSM for 7 Hosts:




These packages are GPG signed by Red Hat for security.  Our key and
details on how to verify the signature are available from

7. References:

8. Contact:

The Red Hat security contact is <>. More contact
details at

Copyright 2016 Red Hat, Inc.
Version: GnuPG v1


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