GHSA-2hwx-mjrm-v3g8

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GHSA-2hwx-mjrm-v3g8

Summary: Denial of service attack via .well-known lookups

Details: ### 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.

References: https://github.com/matrix-org/synapse/security/advisories/GHSA-2hwx-mjrm-v3g8, https://nvd.nist.gov/vuln/detail/CVE-2021-21274, https://github.com/matrix-org/synapse/pull/8950, https://github.com/matrix-org/synapse/commit/ff5c4da1289cb5e097902b3e55b771be342c29d6, https://github.com/matrix-org/synapse, https://github.com/matrix-org/synapse/releases/tag/v1.25.0, https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2021-132.yaml, https://lists.fedoraproject.org/archives/list/[email protected]/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY