CVE-2021-21274

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.

How to fix CVE-2021-21274

To remediate CVE-2021-21274, upgrade the affected package to a fixed version below.

• —upgrade to 1.25.0-1 or later
• —upgrade to 1.25.0 or later
• —upgrade to ff5c4da1289cb5e097902b3e55b771be342c29d6 or later

Is CVE-2021-21274 being exploited?

Low — EPSS is 0.4%, meaning exploitation activity has not been observed at scale.

Affected packages (3)

• from 0, < 1.25.0-1
• >= 0.99.0, < 1.25.0
• from 0, < ff5c4da1289cb5e097902b3e55b771be342c29d6 | >= 0.99.0, < 1.25.0

CVSS scores

References (9)

• ADVISORYnvd.nist.gov/vuln/detail/CVE-2021-21274
• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2021-21274
• PATCHgithub.com/matrix-org/synapse
• WEBgithub.com/matrix-org/synapse/commit/ff5c4da1289cb5e097902b3e55b771be342c29d6
• WEB