Improper access control in Discourse - CVE-2021-43850
Published: January 4, 2022 / Updated: July 1, 2026
Vulnerability identifier: #VU136507
CSH Severity: Medium
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:A/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N/E:U/U:Green
CVE-ID: CVE-2021-43850
CWE-ID: CWE-284
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: Civilized Discourse Construction Kit, Inc.
Affected software:
Discourse
Discourse
Detailed vulnerability description
The vulnerability allows a remote user to cause a denial of service.
The vulnerability exists due to improper access control in the MessageBus::Diagnostics route when handling requests to the /message-bus/_diagnostics path. A remote user can send a request to this path to cause a denial of service.
The impact is greater on multisite instances, where an admin user on any hosted forum can affect the shared application server.
How to mitigate CVE-2021-43850
Install security update from vendor's website.