SB2021120159 - Multiple vulnerabilities in Discourse

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Main Vulnerability Database SB2021120159

SB2021120159 - Multiple vulnerabilities in Discourse

Published: December 1, 2021 Updated: July 1, 2026

Security Bulletin ID SB2021120159
CSH Severity
Medium
Patch available
YES
Number of vulnerabilities 4
Exploitation vector Remote access
Highest impact Denial of service

Breakdown by Severity

Medium 50% Low 50%
  • Low
  • Medium
  • High
  • Critical

Description

This security bulletin contains information about 4 vulnerabilities.


1) Improper access control (CVE-ID: CVE-2021-43850)

CWE-ID: CWE-284 - Improper Access Control

CVSSv4: 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


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.


2) Improper access control (CVE-ID: CVE-2021-43792)

CWE-ID: CWE-284 - Improper Access Control

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:U/U:Clear


The vulnerability allows a remote user to disclose sensitive information.

The vulnerability exists due to improper access control in tag group visibility and notification handling when processing notifications for previously watched tags. A remote user can retain access to notifications for restricted tags after group permissions are revoked to disclose sensitive information.

The issue affects deployments using the "Tags are visible only to the following groups" feature, and occurs when a user was previously tracking or watching the restricted tags before losing access.


3) Improper access control (CVE-ID: CVE-2021-43793)

CWE-ID: CWE-284 - Improper Access Control

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Clear


The vulnerability allows a remote user to bypass poll voting limits.

The vulnerability exists due to improper access control in the Polls feature when submitting votes to a single-option poll. A remote user can submit multiple votes to bypass poll voting limits.


4) Use of Web Browser Cache Containing Sensitive Information (CVE-ID: CVE-2021-43794)

CWE-ID: CWE-525 - Use of Web Browser Cache Containing Sensitive Information

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U/U:Green


The vulnerability allows a remote attacker to cause a partial denial of service.

The vulnerability exists due to improper cache handling in development-mode header processing when handling requests. A remote attacker can send a specially crafted request to cause a partial denial of service.

Anonymous users may be served a JSON blob instead of the expected HTML page.


Remediation

Install update from vendor's website.

References