py-matrix-synapse -- several vulnerabilities

Matrix developers report:

This release patches one high severity issue affecting
Synapse installations 1.47.0 and earlier using the media repository.
An attacker could cause these Synapses to download a remote file
and store it in a directory outside the media repository.
Note that:

This only affects homeservers using Synapse’s built-in media
repository, as opposed to synapse-s3-storage-provider or
matrix-media-repo.
Attackers cannot control the exact name or destination of the
stored file.