CVE-2024-37303: Synapse unauthenticated writes to the media repository allow planting of problematic content
Impact
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.
Patches
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.
Workarounds
Though extremely limited, server operators can use more strict rate limits based on IP address.
References
https://github.com/matrix-org/matrix-spec-proposals/pull/3916
For more information
If you have any questions or comments about this advisory, please email us at security at element.io.
Other sources
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.
— MITRE
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2024-37303?
CVE-2024-37303 is classified with a high severity due to the potential for unauthenticated remote participants to access sensitive media content.
How do I fix CVE-2024-37303?
To remediate CVE-2024-37303, upgrade matrix-synapse to version 1.106 or higher.
Who is affected by CVE-2024-37303?
CVE-2024-37303 affects all versions of Synapse prior to 1.106.
What types of data can be accessed due to CVE-2024-37303?
CVE-2024-37303 allows unauthorized access to remote media that can be downloaded and cached in a local media repository.
Is there a way to prevent CVE-2024-37303 if I cannot update immediately?
To temporarily mitigate CVE-2024-37303, restrict unauthenticated access to your homeserver until an upgrade can be performed.