CVE-2021-43840: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

message_bus is a messaging bus for Ruby processes and web clients. users who deployed message bus with diagnostics features enabled (default off) is 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 Users unable to upgrade should ensure that MessageBus::Diagnostics is disabled.