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Category:   Application (Generic)  >   KVM Vendors:   kvm.qumranet.com
(Red Hat Issues Fix for KVM) Xen Qemu VT100 Emulation Flaw Lets Local Users Gain Elevated Privileges of the Target Device Model Process
SecurityTracker Alert ID:  1027499
SecurityTracker URL:  http://securitytracker.com/id/1027499
CVE Reference:   CVE-2012-3515   (Links to External Site)
Date:  Sep 6 2012
Impact:   User access via local system
Fix Available:  Yes  Vendor Confirmed:  Yes  

Description:   A vulnerability was reported in Xen. A local user on the guest operating system can obtain elevated privileges on the target system. KVM is affected.

Qemu does not properly process escaped VT100 sequences when emulating certain devices with a virtual console backend. A local user on a guest operating system with privileges to access a vulnerable device on that operating system can overwrite portions of the device model's memory. This can be exploited to gain the privileges of the target device model process.

Impact:   A local user on the guest operating system can obtain the privileges of the target device model process.
Solution:   Red Hat has issued a fix for KVM.

The Red Hat advisory is available at:

https://rhn.redhat.com/errata/RHSA-2012-1235.html

Cause:   Input validation error
Underlying OS:  Linux (Red Hat Enterprise)
Underlying OS Comments:  5

Message History:   This archive entry is a follow-up to the message listed below.
Sep 5 2012 Xen Qemu VT100 Emulation Flaw Lets Local Users Gain Elevated Privileges of the Target Device Model Process



 Source Message Contents

Subject:  [RHSA-2012:1235-01] Important: kvm security update

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=====================================================================
                   Red Hat Security Advisory

Synopsis:          Important: kvm security update
Advisory ID:       RHSA-2012:1235-01
Product:           Red Hat Enterprise Linux
Advisory URL:      https://rhn.redhat.com/errata/RHSA-2012-1235.html
Issue date:        2012-09-05
CVE Names:         CVE-2012-3515 
=====================================================================

1. Summary:

Updated kvm packages that fix one security issue are now available for
Red Hat Enterprise Linux 5.

The Red Hat Security Response Team has rated this update as having
important 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:

RHEL Desktop Multi OS (v. 5 client) - x86_64
RHEL Virtualization (v. 5 server) - x86_64

3. Description:

KVM (Kernel-based Virtual Machine) is a full virtualization solution for
Linux on AMD64 and Intel 64 systems. KVM is a Linux kernel module built
for the standard Red Hat Enterprise Linux kernel.

A flaw was found in the way QEMU handled VT100 terminal escape sequences
when emulating certain character devices. A guest user with privileges to
write to a character device that is emulated on the host using a virtual
console back-end could use this flaw to crash the qemu-kvm process on the
host or, possibly, escalate their privileges on the host. (CVE-2012-3515)

This flaw did not affect the default use of KVM. Affected configurations
were:

* When guests were started from the command line ("/usr/libexec/qemu-kvm"),
and without specifying a serial or parallel device that specifically does
not use a virtual console (vc) back-end. (Note that Red Hat does not
support invoking "qemu-kvm" from the command line on Red Hat Enterprise
Linux 5.)

* Guests that were managed via libvirt, such as when using Virtual Machine
Manager (virt-manager), but that have a serial or parallel device that uses
a virtual console back-end. By default, guests managed via libvirt will not
use a virtual console back-end for such devices.

Red Hat would like to thank the Xen project for reporting this issue.

All KVM users should upgrade to these updated packages, which correct this
issue. Note: The procedure in the Solution section must be performed before
this update will take effect.

4. Solution:

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

This update is available via the Red Hat Network. Details on how to
use the Red Hat Network to apply this update are available at
https://access.redhat.com/knowledge/articles/11258

The following procedure must be performed before this update will take
effect:

1) Stop all KVM guest virtual machines.

2) Either reboot the hypervisor machine or, as the root user, remove (using
"modprobe -r [module]") and reload (using "modprobe [module]") all of the
following modules which are currently running (determined using "lsmod"):
kvm, ksm, kvm-intel or kvm-amd.

3) Restart the KVM guest virtual machines.

5. Bugs fixed (http://bugzilla.redhat.com/):

851252 - CVE-2012-3515 qemu: VT100 emulation vulnerability

6. Package List:

RHEL Desktop Multi OS (v. 5 client):

Source:
ftp://ftp.redhat.com/pub/redhat/linux/enterprise/5Client/en/os/SRPMS/kvm-83-249.el5_8.5.src.rpm

x86_64:
kmod-kvm-83-249.el5_8.5.x86_64.rpm
kmod-kvm-debug-83-249.el5_8.5.x86_64.rpm
kvm-83-249.el5_8.5.x86_64.rpm
kvm-debuginfo-83-249.el5_8.5.x86_64.rpm
kvm-qemu-img-83-249.el5_8.5.x86_64.rpm
kvm-tools-83-249.el5_8.5.x86_64.rpm

RHEL Virtualization (v. 5 server):

Source:
ftp://ftp.redhat.com/pub/redhat/linux/enterprise/5Server/en/os/SRPMS/kvm-83-249.el5_8.5.src.rpm

x86_64:
kmod-kvm-83-249.el5_8.5.x86_64.rpm
kmod-kvm-debug-83-249.el5_8.5.x86_64.rpm
kvm-83-249.el5_8.5.x86_64.rpm
kvm-debuginfo-83-249.el5_8.5.x86_64.rpm
kvm-qemu-img-83-249.el5_8.5.x86_64.rpm
kvm-tools-83-249.el5_8.5.x86_64.rpm

These packages are GPG signed by Red Hat for security.  Our key and
details on how to verify the signature are available from
https://access.redhat.com/security/team/key/#package

7. References:

https://www.redhat.com/security/data/cve/CVE-2012-3515.html
https://access.redhat.com/security/updates/classification/#important

8. Contact:

The Red Hat security contact is <secalert@redhat.com>.  More contact
details at https://access.redhat.com/security/team/contact/

Copyright 2012 Red Hat, Inc.
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