CVE-2021-21274
In Synapse before version 1.25.0, a malicious homeserver could redirect requests to their .well-known file to a large file.
Does this matter?
Lower severity and a low EPSS score (2.16%). Track it; it rarely justifies an emergency change on its own.
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.
- CVSS 3.1
- 6.5 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
- EPSS
- 2.16% probability · 81th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-400, CWE-770
- Affected
- matrix/synapse · fedoraproject/fedora
- Source
- security-advisories@github.com
References
- https://github.com/matrix-org/synapse/commit/ff5c4da1289cb5e097902b3e55b771be342c29d6Patch, Third Party Advisory
- https://github.com/matrix-org/synapse/pull/8950Patch, Third Party Advisory
- https://github.com/matrix-org/synapse/releases/tag/v1.25.0Third Party Advisory
- https://github.com/matrix-org/synapse/security/advisories/GHSA-2hwx-mjrm-v3g8Patch, Third Party Advisory
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/
- https://github.com/matrix-org/synapse/commit/ff5c4da1289cb5e097902b3e55b771be342c29d6Patch, Third Party Advisory
- https://github.com/matrix-org/synapse/pull/8950Patch, Third Party Advisory
- https://github.com/matrix-org/synapse/releases/tag/v1.25.0Third Party Advisory
- https://github.com/matrix-org/synapse/security/advisories/GHSA-2hwx-mjrm-v3g8Patch, Third Party Advisory
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.