CVE-2023-32683

Synapse is a Matrix protocol homeserver written in Python with the Twisted
framework. A discovered oEmbed or image URL can bypass the
url_preview_url_blacklist setting potentially allowing server side
request forgery or bypassing network policies. Impact is limited to IP
addresses allowed by the url_preview_ip_range_blacklist setting (by
default this only allows public IPs) and by the limited information
returned to the client: 1. For discovered oEmbed URLs, any non-JSON
response or a JSON response which includes non-oEmbed information is
discarded. 2. For discovered image URLs, any non-image response is
discarded. Systems which have URL preview disabled (via the
url_preview_enabled setting) or have not configured a
url_preview_url_blacklist are not affected. This issue has been addressed
in version 1.85.0. Users are advised to upgrade. User unable to upgrade may
also disable URL previews.