CVE-2021-21274
4.3 · MEDIUMOverview
CVE-2021-21274 is a medium-severity vulnerability affecting matrix synapse. It was published on February 26, 2021 and has a CVSS 3.1 base score of 4.3 (MEDIUM).
This vulnerability has a CVSS 3.1 base score of 4.3, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
Technical 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.
Remediation
Check the references section for vendor advisories and patches from matrix. Update synapse to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
Affected Products
| Vendor | Product | Versions | Status |
|---|---|---|---|
| matrix | synapse | >= 0.99.0, < 1.25.0 | Affected |
References
Frequently Asked Questions
What is CVE-2021-21274?
CVE-2021-21274 is a medium-severity vulnerability affecting matrix synapse. It was published on February 26, 2021 and has a CVSS 3.1 base score of 4.3 (MEDIUM).
How severe is CVE-2021-21274?
This vulnerability has a CVSS 3.1 base score of 4.3, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
How do I fix or remediate CVE-2021-21274?
Check the references section for vendor advisories and patches from matrix. Update synapse to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
How can CyberStrike help with CVE-2021-21274?
CyberStrike's AI-powered security agents can automatically detect CVE-2021-21274 across your infrastructure using autonomous pentesting, DAST scanning, and HackBrowser. The platform continuously monitors for known vulnerabilities and provides actionable remediation guidance prioritized by real-world exploitability.
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