CVE-2024-37303: Synapse unauthenticated writes to the media repository allow planting of problematic content

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-12-03 · updated 2026-06-17
Weakness: CWE-306

Description

Synapse is an open-source Matrix homeserver. Synapse before version 1.106 allows, by design, unauthenticated remote participants to trigger a download and caching of remote media from a remote homeserver to the local media repository. Such content then also becomes available for download from the local homeserver in an unauthenticated way. The implication is that unauthenticated remote adversaries can use this functionality to plant problematic content into the media repository. Synapse 1.106 introduces a partial mitigation in the form of new endpoints which require authentication for media downloads. The unauthenticated endpoints will be frozen in a future release, closing the attack vector.

Affected products

matrix-org synapse: before 1.106.0 — fixed in 1.106.0

How to fix

Upgrade to a fixed version: matrix-org synapse 1.106.0. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2024-37303 or the next vulnerability affects your stack