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CVE-2021-43840

4.4 · MEDIUM

message_bus is a messaging bus for Ruby processes and web clients.

Published Dec 17, 2021CWE-22EPSS 1.95%

Overview

CVE-2021-43840 is a medium-severity vulnerability. It was published on December 17, 2021 and has a CVSS 3.1 base score of 4.4 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 4.4, rated MEDIUM. It can be exploited remotely over the network. Some level of privileges is required for exploitation.

Technical description

message_bus is a messaging bus for Ruby processes and web clients. In versions prior to 3.3.7 users who deployed message bus with diagnostics features enabled (default off) are vulnerable to a path traversal bug, which could lead to disclosure of secret information on a machine if an unintended user were to gain access to the diagnostic route. The impact is also greater if there is no proxy for your web application as the number of steps up the directories is not bounded. For deployments which uses a proxy, the impact varies. For example, If a request goes through a proxy like Nginx with `merge_slashes` enabled, the number of steps up the directories that can be read is limited to 3 levels. This issue has been patched in version 3.3.7. Users unable to upgrade should ensure that MessageBus::Diagnostics is disabled.

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/discourse/message_bus/commit/9b6deee01ed474c7e9b5ff65a06bb0447b4db2baGitHubgithub.com/discourse/message_bus/security/advisories/GHSA-xmgj-5fh3-xjmmGitHubgithub.com/discourse/message_bus/commit/9b6deee01ed474c7e9b5ff65a06bb0447b4db2baGitHubgithub.com/discourse/message_bus/security/advisories/GHSA-xmgj-5fh3-xjmm

How CyberStrike helps

Frequently asked questions

What is CVE-2021-43840?

CVE-2021-43840 is a medium-severity vulnerability. It was published on December 17, 2021 and has a CVSS 3.1 base score of 4.4 (MEDIUM).

How severe is CVE-2021-43840?

This vulnerability has a CVSS 3.1 base score of 4.4, 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-2021-43840?

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-2021-43840?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2021-43840 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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