X.Org Security Advisory: Issues in X.Org X server prior to 21.1.10 and Xwayland prior to 23.2.3

[Peter Hutterer]

X.Org Security Advisory: December 13, 2023

Issues in X.Org X server prior to 21.1.10 and Xwayland prior to 23.2.3
========================================================================

Multiple issues have been found in the X server and Xwayland implementations 
published by X.Org for which we are releasing security fixes for in
xorg-server-21.1.10 and xwayland-23.2.3.

1) CVE-2023-6377 can be triggered by forcing a logical device change on a device
with buttons which will result in an out-of-bounds memory write.

2) CVE-2023-6478 can be triggered by sending a specially crafted
request RRChangeProviderProperty or RRChangeOutputProperty. This will trigger
an integer overflow and lead to disclosure of information.

------------------------------------------------------------------------

1) CVE-2023-6377: X.Org server: Out-of-bounds memory write in XKB button actions

Introduced in: xorg-server-1.6.0 (2009)
Fixed in: xorg-server-21.1.10 and xwayland-23.2.3
Fix: https://gitlab.freedesktop.org/xorg/xserver/-/commit/0c1a93d319558fe3ab2d94f51d174b4f93810afd
Found by: Jan-Niklas Sohn working with Trend Micro Zero Day Initiative

A device has XKB button actions for each button on the device. When a logical
device switch happens (e.g. moving from a touchpad to a mouse), the server 
re-calculates the information available on the respective master device
(typically the Virtual Core Pointer). This re-calculation only allocated enough
memory for a single XKB action rather instead of enough for the newly active
physical device's number of button. As a result, querying or changing the XKB
button actions results in out-of-bounds memory reads and writes.

This may lead to local privilege escalation if the server is run as root or
remote code execution (e.g. x11 over ssh).

xorg-server-21.1.10 and xwayland-23.2.3 have been patched to fix this issue.


2) CVE-2023-6478: X.Org server: Out-of-bounds memory read in RRChangeOutputProperty and RRChangeProviderProperty

Introduced in: xorg-server-1.4.0 (2007) and xorg-server-1.13.0 (2012), respectively
Fixed in: xorg-server-21.1.10 and xwayland-23.2.3
Fix: https://gitlab.freedesktop.org/xorg/xserver/-/commit/14f480010a93ff962fef66a16412fafff81ad632
Found by: Jan-Niklas Sohn working with Trend Micro Zero Day Initiative

This fixes an OOB read and the resulting information disclosure.

Length calculation for the request was clipped to a 32-bit integer. With
the correct stuff->nUnits value the expected request size was
truncated, passing the REQUEST_FIXED_SIZE check.

The server then proceeded with reading at least stuff->nUnits bytes
(depending on stuff->format) from the request and stuffing whatever it
finds into the property. In the process it would also allocate at least
stuff->nUnits bytes, i.e. 4GB.

See also CVE-2022-46344 where this issue was fixed for other requests.

xorg-server-21.1.10 and xwayland-23.2.3 have been patched to fix this issue.

------------------------------------------------------------------------

X.Org thanks all of those who reported and fixed these issues, and those
who helped with the review and release of this advisory and these fixes.
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