{"cve":"CVE-2021-43840","nvd":{"published":"2021-12-17T19:15:07.757","modified":"2026-06-17T04:11:32.900","status":"Modified","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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N","score":6.5},"cwes":["CWE-22"],"references":["https://github.com/discourse/message_bus/commit/9b6deee01ed474c7e9b5ff65a06bb0447b4db2ba","https://github.com/discourse/message_bus/security/advisories/GHSA-xmgj-5fh3-xjmm","https://github.com/discourse/message_bus/commit/9b6deee01ed474c7e9b5ff65a06bb0447b4db2ba","https://github.com/discourse/message_bus/security/advisories/GHSA-xmgj-5fh3-xjmm"],"products":["discourse:message_bus"],"source":"nvd","synced_at":"2026-10-19T21:25:41.256909649+00:00"},"epss":{"cve":"CVE-2021-43840","score":0.01947,"percentile":0.80193,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-xmgj-5fh3-xjmm","url":"https://osv.dev/vulnerability/GHSA-xmgj-5fh3-xjmm","summary":"Path traversal when MessageBus::Diagnostics is enabled","modified":"2026-07-08T06:29:06.303929406Z","packages":[{"ecosystem":"RubyGems","name":"message_bus","purl":"pkg:gem/message_bus","ranges":["<3.3.7"],"fixed":["3.3.7"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}