CVE-2023-32683: Matrix Synapse

Medium severity, CVSS 5.4. EPSS: 0.6% chance of exploitation in the next 30 days.

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.

Affected products

• Matrix Synapse: before 1.85.0 (fixed in 1.85.0)

Published 2023-06-06. Last modified 2026-06-17.