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Ubuntu Security Notice USN-3453-1
October 12, 2017

xorg-server, xorg-server-hwe-16.04, xorg-server-lts-xenial vulnerabilities
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A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 17.04
- Ubuntu 16.04 LTS
- Ubuntu 14.04 LTS

Summary:

Several security issues were fixed in the X.Org X server.

Software Description:
- xorg-server: X.Org X11 server
- xorg-server-hwe-16.04: X.Org X11 server
- xorg-server-lts-xenial: X.Org X11 server

Details:

Michal Srb discovered that the X.Org X server incorrectly handled shared
memory segments. An attacker able to connect to an X server, either locally
or remotely, could use this issue to crash the server, or possibly replace
shared memory segments of other X clients in the same session.
(CVE-2017-13721)

Michal Srb discovered that the X.Org X server incorrectly handled XKB
buffers. An attacker able to connect to an X server, either locally or
remotely, could use this issue to crash the server, or possibly execute
arbitrary code. (CVE-2017-13723)

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 17.04:
  xserver-xorg-core               2:1.19.3-1ubuntu1.2

Ubuntu 16.04 LTS:
  xserver-xorg-core               2:1.18.4-0ubuntu0.6
  xserver-xorg-core-hwe-16.04     2:1.19.3-1ubuntu1~16.04.3

Ubuntu 14.04 LTS:
  xserver-xorg-core               2:1.15.1-0ubuntu2.10
  xserver-xorg-core-lts-xenial    2:1.18.3-1ubuntu2.3~trusty3

After a standard system update you need to reboot your computer to make
all the necessary changes.

References:
  https://www.ubuntu.com/usn/usn-3453-1
  CVE-2017-13721, CVE-2017-13723

Package Information:
  https://launchpad.net/ubuntu/+source/xorg-server/2:1.19.3-1ubuntu1.2
  https://launchpad.net/ubuntu/+source/xorg-server/2:1.18.4-0ubuntu0.6

https://launchpad.net/ubuntu/+source/xorg-server-hwe-16.04/2:1.19.3-1ubuntu1~16.04.3
  https://launchpad.net/ubuntu/+source/xorg-server/2:1.15.1-0ubuntu2.10

https://launchpad.net/ubuntu/+source/xorg-server-lts-xenial/2:1.18.3-1ubuntu2.3~trusty3