In short
- CVE-2021-21274 is a MEDIUM (CVSS 6.5) vulnerability affecting matrix-synapse, synapse (matrix).
- Chance of exploitation in the next 30 days (EPSS): 2.2%, higher than 82.2% of all vulnerabilities.
- Fix: update to 1.25.0 or later.
| Package | Affected versions | Patched versions |
|---|
| matrix-synapse PyPI | ≥ 0.99.0, < 1.25.0
| 1.25.0
|
| synapse | ≥ 0.99.0, < 1.25.0
| 1.25.0
|
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.
NVD 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.
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