[ASA-201901-12] matrix-synapse: private key recovery

[Morten Linderud]

Arch Linux Security Advisory ASA-201901-12
==========================================

Severity: High
Date    : 2019-01-24
CVE-ID  : CVE-2019-5885
Package : matrix-synapse
Type    : private key recovery
Remote  : No
Link    : https://security.archlinux.org/AVG-846

Summary
=======

The package matrix-synapse before version 0.34.1.1-1 is vulnerable to
private key recovery.

Resolution
==========

Upgrade to 0.34.1.1-1.

# pacman -Syu "matrix-synapse>=0.34.1.1-1"

The problem has been fixed upstream in version 0.34.1.1.

Workaround
==========

None.

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

matrix-synapse before 0.34.1 is vulnerable to private key recovery as
synapse will attempt to derive a secret key from other secrets
specified in the configuration file for "macaroon_secret_key". However,
in all versions of Synapse up to and including 0.34.0, this process was
faulty and a predictable value was used instead.

Impact
======

If no private key is specified a predictable key is used allowing
private key recover.

References
==========

https://matrix.org/blog/2019/01/15/further-details-on-critical-security-update-in-synapse-affecting-all-versions-prior-to-0-34-1-cve-2019-5885/
https://security.archlinux.org/CVE-2019-5885
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