Vulnerability CVE-2021-21274


Published: 2021-02-26

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.

Type:

CWE-400

(Uncontrolled Resource Consumption ('Resource Exhaustion'))

CVSS2 => (AV:N/AC:M/Au:N/C:N/I:N/A:P)

CVSS Base Score
Impact Subscore
Exploitability Subscore
4.3/10
2.9/10
8.6/10
Exploit range
Attack complexity
Authentication
Remote
Medium
No required
Confidentiality impact
Integrity impact
Availability impact
None
None
Partial
Affected software
Matrix -> Synapse 

 References:
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

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