Bug 1894657 (CVE-2020-28049) - CVE-2020-28049 sddm: local privilege escalation due to race condition in creation of the Xauthority file
Summary: CVE-2020-28049 sddm: local privilege escalation due to race condition in crea...
Alias: CVE-2020-28049
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
Target Milestone: ---
Assignee: Red Hat Product Security
QA Contact:
Depends On: 1894659 1894658
TreeView+ depends on / blocked
Reported: 2020-11-04 17:36 UTC by Guilherme de Almeida Suckevicz
Modified: 2020-11-04 20:21 UTC (History)
6 users (show)

Fixed In Version:
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Last Closed: 2020-11-04 20:21:44 UTC

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Description Guilherme de Almeida Suckevicz 2020-11-04 17:36:08 UTC
sddm passes the -auth and -displayfd command line arguments when
starting the Xserver. It then waits for the display number to be
received from the Xserver via the `displayfd`, before the Xauthority
file specified via the `-auth` parameter is actually written. This
results in a race condition, creating a time window in which no valid
Xauthority file is existing while the Xserver is already running.

The X.Org server, when encountering a non-existing, empty or
corrupt/incomplete Xauthority file, will grant any connecting client
access to the Xorg display [2]. A local unprivileged attacker can thus
create an unauthorized connection to the Xserver and grab e.g. keyboard
input events from other legitimate users accessing the Xserver.


Comment 1 Guilherme de Almeida Suckevicz 2020-11-04 17:36:26 UTC
Created sddm tracking bugs for this issue:

Affects: epel-all [bug 1894659]
Affects: fedora-all [bug 1894658]

Comment 2 Product Security DevOps Team 2020-11-04 20:21:44 UTC
This CVE Bugzilla entry is for community support informational purposes only as it does not affect a package in a commercially supported Red Hat product. Refer to the dependent bugs for status of those individual community products.

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