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Category:   Application (Generic)  >   Red Hat Enterprise Virtualization Vendors:   Red Hat
(Red Hat Issues Fix for Red Hat Enterprise Virtualization) QEMU VNC Websockets Decoder Lets Remote Users on the Local Network Consume Excessive Memory and CPU Resources
SecurityTracker Alert ID:  1033978
SecurityTracker URL:
CVE Reference:   CVE-2015-1779   (Links to External Site)
Date:  Oct 27 2015
Impact:   Denial of service via network
Fix Available:  Yes  Vendor Confirmed:  Yes  

Description:   A vulnerability was reported in QEMU. A remote user on the local network can consume excessive memory and CPU resources on the target system. Red Hat Enterprise Virtualization is affected.

A remote user on the local network can send specially crafted data to the target VNC websockets protocol decoder to cause QEMU to consume all available system memory.

Daniel P. Berrange of Red Hat reported this vulnerability.

Impact:   A remote user can consume excessive memory and CPU resources on the target 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.
Oct 27 2015 QEMU VNC Websockets Decoder Lets Remote Users on the Local Network Consume Excessive Memory and CPU Resources

 Source Message Contents

Subject:  [RHSA-2015:1931-01] Moderate: qemu-kvm-rhev security update

Hash: SHA1

                   Red Hat Security Advisory

Synopsis:          Moderate: qemu-kvm-rhev security update
Advisory ID:       RHSA-2015:1931-01
Product:           Red Hat Enterprise Virtualization
Advisory URL:
Issue date:        2015-10-26
CVE Names:         CVE-2015-1779 

1. Summary:

Updated qemu-kvm-rhev packages that fix one security issue are now
available for Red Hat Enterprise Virtualization Hypervisor 7.

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

2. Relevant releases/architectures:

RHEV-H and VDSM for 7 Hosts - 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.

It was found that the QEMU's websocket frame decoder processed incoming
frames without limiting resources used to process the header and the
payload. An attacker able to access a guest's VNC console could use this
flaw to trigger a denial of service on the host by exhausting all available
memory and CPU. (CVE-2015-1779)

This issue was discovered by Daniel P. Berrange of Red Hat.

All qemu-kvm-rhev users are advised to upgrade to these updated packages,
which contain a backported patch to correct this issue. 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.

4. Solution:

Before applying this update, make sure all previously released errata
relevant to your system have been applied.

For details on how to apply this update, refer to:

5. Bugs fixed (

1199572 - CVE-2015-1779 qemu: vnc: insufficient resource limiting in VNC websockets decoder

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 2015 Red Hat, Inc.
Version: GnuPG v1


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