Description

Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.25.0, a malicious homeserver could redirect requests to their .well-known file to a large file. This can lead to a denial of service attack where homeservers will consume significantly more resources when requesting the .well-known file of a malicious homeserver. This affects any server which accepts federation requests from untrusted servers. Issue is resolved in version 1.25.0. As a workaround the `federation_domain_whitelist` setting can be used to restrict the homeservers communicated with over federation.

References

https://github.com/matrix-org/synapse/commit/ff5c4da1289cb5e097902b3e55b771be342c29d6

https://github.com/matrix-org/synapse/pull/8950

https://github.com/matrix-org/synapse/releases/tag/v1.25.0

https://github.com/matrix-org/synapse/security/advisories/GHSA-2hwx-mjrm-v3g8

Details

Risk Information

CVSS v2.0

CVSS v3.0