matrix-org/synapse · Security
Denial of service attack via .well-known lookups
- GHSA ID
- GHSA-2hwx-mjrm-v3g8
- CVE ID
- CVE-2021-21274
- Severity
- medium
- Published
- Updated
- CVSS
- 4.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L
- CVSS v3
- 4.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L
- CVSS v4
- 5.3 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
Description
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.
CWEs
- CWE-400 · Uncontrolled Resource Consumption
- CWE-770 · Allocation of Resources Without Limits or Throttling
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/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 ↗
- https://github.com/advisories/GHSA-2hwx-mjrm-v3g8 ↗