ASA-202011-23: matrix-synapse: denial of service

Arch Linux Security Advisory ASA-202011-23
=========================================
Severity: High
Date : 2020-11-26
CVE-ID : CVE-2020-26890
Package : matrix-synapse
Type : denial of service
Remote : Yes
Link :   https://security.archlinux.org/AVG-1296

Summary
======
The package matrix-synapse before version 1.20.1-1 is vulnerable to
denial of service.

Resolution
=========
Upgrade to 1.20.1-1.

# pacman -Syu "matrix-synapse>=1.20.1-1"

The problem has been fixed upstream in version 1.20.1.

Workaround
=========
None.

Description
==========
Matrix Synapse before 1.20.0 erroneously permits non-standard NaN,
Infinity, and -Infinity JSON values in fields of m.room.member events,
allowing remote attackers to execute a denial of service attack against
the federation and common Matrix clients. If such a malformed event is
accepted into the room's state, the impact is long-lasting and is not
fixed by an upgrade to a newer version, requiring the event to be
manually redacted instead. Since events are replicated to servers of
other room members, the impact is not constrained to the server of the
event sender.

Impact
=====
A remote attacker might be able to cause a denial of service via a
crafted event.

References
=========
  https://github.com/matrix-org/synapse/security/advisories/GHSA-4mp3-385r-v63f
  https://github.com/matrix-org/synapse/pull/8106
  https://github.com/matrix-org/synapse/pull/8106/commits/c88c15b5fcf26940515b0f6398981ea5fab25347
  https://github.com/matrix-org/synapse/pull/8106/commits/248d8284fa850289689f9ae87d2c807b58d7a812
  https://github.com/matrix-org/synapse/pull/8106/commits/5516ae216d8cfe34b04ad190d8ec3c50bec07835
  https://github.com/matrix-org/synapse/pull/8291
  https://github.com/matrix-org/synapse/pull/8291/commits/1cad688bda57dcc8f9c09dff30fcbce818a3a20d
  https://github.com/matrix-org/synapse/pull/8291/commits/4d654058dec5a77e2d1c50251ac8cd86c2e8e98f
  https://security.archlinux.org/CVE-2020-26890