First published: Fri Feb 26 2021(Updated: )
### Impact 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. ### Patches Issue is resolved by #8950. A bug not affecting the security aspects of this was fixed in #9108. ### Workarounds The `federation_domain_whitelist` setting can be used to restrict the homeservers communicated with over federation.
Credit: security-advisories@github.com security-advisories@github.com
Affected Software | Affected Version | How to fix |
---|---|---|
Matrix Synapse | >=0.99.0<1.25.0 | |
Fedoraproject Fedora | =34 | |
pip/matrix-synapse | >=0.99.0<1.25.0 | 1.25.0 |
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CVE-2021-21274 is a vulnerability in Synapse, a Matrix reference homeserver, that allows a malicious server to redirect requests to a large file.
Synapse is a Matrix reference homeserver written in Python that provides an ecosystem for open federated Instant Messaging and VoIP.
CVE-2021-21274 has a severity of 6.5 (Medium).
CVE-2021-21274 can be fixed by upgrading to Synapse version 1.25.0 or later.
Yes, you can find references for CVE-2021-21274 at the following links: [GitHub Commit](https://github.com/matrix-org/synapse/commit/ff5c4da1289cb5e097902b3e55b771be342c29d6), [GitHub Pull Request](https://github.com/matrix-org/synapse/pull/8950), [GitHub Release](https://github.com/matrix-org/synapse/releases/tag/v1.25.0).