Arch Linux Security Advisory ASA-201710-10
==========================================

Severity: Medium
Date    : 2017-10-08
CVE-ID  : CVE-2017-13721 CVE-2017-13723
Package : xorg-server
Type    : multiple issues
Remote  : No
Link    : https://security.archlinux.org/AVG-432

Summary
=======

The package xorg-server before version 1.19.4-1 is vulnerable to
multiple issues including arbitrary code execution and denial of
service.

Resolution
==========

Upgrade to 1.19.4-1.

# pacman -Syu "xorg-server>=1.19.4-1"

The problems have been fixed upstream in version 1.19.4.

Workaround
==========

None.

Description
===========

- CVE-2017-13721 (denial of service)

A denial of service vulnerability was found in xorg-server in the
ProcShmCreateSegment function due to a missing shmseg resource ids
validation. A passed shmseg resource id may belong to a non-existing
client and abort X server with FatalError "client not in use", or
overwrite existing segment of another existing client.

- CVE-2017-13723 (arbitrary code execution)

A stack buffer overflow was found in xkbtext.c, which didn't handle xkb
formatted string output safely due to a single shared static buffer.
The fix introduces a ring of resizable buffers to avoid problems when
strings end up longer than anticipated.
This vulnerability may potentially lead to privilege escalation when
the xorg-server is running with root privileges.

Impact
======

A local attacker is able to crash the xorg-server process leading to
denial of service or possibly elevate privileges when the xorg-server
is running with root privileges.

References
==========

https://lists.x.org/archives/xorg-announce/2017-October/002808.html
https://cgit.freedesktop.org/xorg/xserver/commit/?id=b95f25af141d33a65f6f821ea9c003f66a01e1f1
https://cgit.freedesktop.org/xorg/xserver/commit/?id=94f11ca5cf011ef123bd222cabeaef6f424d76ac
https://security.archlinux.org/CVE-2017-13721
https://security.archlinux.org/CVE-2017-13723