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CVE-2021-21392

6.3 · MEDIUM

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

Published Apr 12, 2021CWE-601EPSS 0.94%

Overview

CVE-2021-21392 is a medium-severity vulnerability. It was published on April 12, 2021 and has a CVSS 3.1 base score of 6.3 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 6.3, rated MEDIUM. It can be exploited remotely over the network. Some level of privileges is 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 1.28.0 requests to user provided domains were not restricted to external IP addresses when transitional IPv6 addresses were used. Outbound requests to federation, identity servers, when calculating the key validity for third-party invite events, sending push notifications, and generating URL previews are affected. This could cause Synapse to make requests to internal infrastructure on dual-stack networks. See referenced GitHub security advisory for details and workarounds.

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/pull/9240GitHubgithub.com/matrix-org/synapse/security/advisories/GHSA-5wrh-4jwv-5w78Reflists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/Refpypi.org/project/matrix-synapse/GitHubgithub.com/matrix-org/synapse/pull/9240GitHubgithub.com/matrix-org/synapse/security/advisories/GHSA-5wrh-4jwv-5w78Reflists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/Refpypi.org/project/matrix-synapse/

How CyberStrike helps

Frequently asked questions

What is CVE-2021-21392?

CVE-2021-21392 is a medium-severity vulnerability. It was published on April 12, 2021 and has a CVSS 3.1 base score of 6.3 (MEDIUM).

How severe is CVE-2021-21392?

This vulnerability has a CVSS 3.1 base score of 6.3, rated MEDIUM. It can be exploited remotely over the network. Some level of privileges is required for exploitation.

How do I fix or remediate CVE-2021-21392?

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-2021-21392?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2021-21392 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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