medium4.3
CVE-2021-21274
Denial of service attack via .well-known lookups
Impact
### 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.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| pip | matrix-synapse | >= 0.99.0, < 1.25.0 | 1.25.0 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Matrix | Synapse | from 0.99.0 before 1.25.0 |
| Fedoraproject | Fedora | Version 34 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/matrix-org/synapse/commit/ff5c4da1289cb5e097902b3e55b771be342c29d6
- https://github.com/matrix-org/synapse/pull/8950
- https://github.com/matrix-org/synapse/releases/tag/v1.25.0
- https://github.com/matrix-org/synapse/security/advisories/GHSA-2hwx-mjrm-v3g8
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/
- https://github.com/advisories/GHSA-2hwx-mjrm-v3g8
- https://nvd.nist.gov/vuln/detail/CVE-2021-21274
- https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2021-132.yaml
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY