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CVE-2021-21273

3.1 · LOW

Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse).

Published Feb 26, 2021CWE-601EPSS 1.80%

Overview

CVE-2021-21273 is a low-severity vulnerability. 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, patches, and mitigation guidance. 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.

References

GitHubgithub.com/matrix-org/synapse/commit/30fba6210834a4ecd91badf0c8f3eb278b72e746GitHubgithub.com/matrix-org/synapse/pull/8821GitHubgithub.com/matrix-org/synapse/releases/tag/v1.25.0GitHubgithub.com/matrix-org/synapse/security/advisories/GHSA-v936-j8gp-9q3pReflists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/GitHubgithub.com/matrix-org/synapse/commit/30fba6210834a4ecd91badf0c8f3eb278b72e746GitHubgithub.com/matrix-org/synapse/pull/8821GitHubgithub.com/matrix-org/synapse/releases/tag/v1.25.0GitHubgithub.com/matrix-org/synapse/security/advisories/GHSA-v936-j8gp-9q3pReflists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/

How CyberStrike helps

Frequently asked questions

What is CVE-2021-21273?

CVE-2021-21273 is a low-severity vulnerability. 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, patches, and mitigation guidance. 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 is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2021-21273 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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