CVE-2021-21274: Denial of service attack via .well-known lookups
(updated )
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.
References
- github.com/advisories/GHSA-2hwx-mjrm-v3g8
- github.com/matrix-org/synapse
- github.com/matrix-org/synapse/commit/ff5c4da1289cb5e097902b3e55b771be342c29d6
- github.com/matrix-org/synapse/pull/8950
- github.com/matrix-org/synapse/releases/tag/v1.25.0
- github.com/matrix-org/synapse/security/advisories/GHSA-2hwx-mjrm-v3g8
- github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2021-132.yaml
- lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY
- nvd.nist.gov/vuln/detail/CVE-2021-21274
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