CVE-2021-21273
3.1 · LOWOverview
CVE-2021-21273 is a low-severity vulnerability affecting matrix synapse. It was published on February 26, 2021 and has a CVSS 3.1 base score of 3.1 (LOW).
This vulnerability has a CVSS 3.1 base score of 3.1, rated LOW. 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, requests to user provided domains were not restricted to external IP addresses when calculating the key validity for third-party invite events and sending push notifications. This could cause Synapse to make requests to internal infrastructure. The type of request was not controlled by the user, although limited modification of request bodies was possible. For the most thorough protection server administrators should remove the deprecated `federation_ip_range_blacklist` from their settings after upgrading to Synapse v1.25.0 which will result in Synapse using the improved default IP address restrictions. See the new `ip_range_blacklist` and `ip_range_whitelist` settings if more specific control is necessary.
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, < 1.25.0 | Affected |
References
Frequently Asked Questions
What is CVE-2021-21273?
CVE-2021-21273 is a low-severity vulnerability affecting matrix synapse. It was published on February 26, 2021 and has a CVSS 3.1 base score of 3.1 (LOW).
How severe is CVE-2021-21273?
This vulnerability has a CVSS 3.1 base score of 3.1, rated LOW. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
How do I fix or remediate CVE-2021-21273?
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-2021-21273?
CyberStrike's AI-powered security agents can automatically detect CVE-2021-21273 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.
How CyberStrike Helps
AI agents map your attack surface to find vulnerabilities like this one.
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