A matrix-synapse security update has been released for Arch Linux.

Arch Linux Security Advisory ASA-202011-4
=========================================

Severity: High
Date : 2020-11-03
CVE-ID : CVE-2020-26891
Package : matrix-synapse
Type : cross-site scripting
Remote : Yes
Link :   https://security.archlinux.org/AVG-1252

Summary
=======

The package matrix-synapse before version 1.21.0-1 is vulnerable to
cross-site scripting.

Resolution
==========

Upgrade to 1.21.0-1.

# pacman -Syu "matrix-synapse>=1.21.0-1"

The problem has been fixed upstream in version 1.21.0.

Workaround
==========

None.

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

A security issue has been found in matrix-synapse before 1.21.0, where
HTML pages served via Synapse were vulnerable to cross-site scripting
(XSS) attacks.

Impact
======

A remote attacker might be able to spoof content and execute code via a
cross-site scripting attack.

References
==========

  https://github.com/matrix-org/synapse/releases/tag/v1.21.2
  https://github.com/matrix-org/synapse/pull/8444
  https://security.archlinux.org/CVE-2020-26891