CVE-2022-21684 in Discourse
Summary
by MITRE • 01/14/2022
Discourse is an open source discussion platform. Versions prior to 2.7.13 in `stable`, 2.8.0.beta11 in `beta`, and 2.8.0.beta11 in `tests-passed` allow some users to log in to a community before they should be able to do so. A user invited via email to a forum with `must_approve_users` enabled is going to be automatically logged in, bypassing the check that does not allow unapproved users to sign in. They will be able to do everything an approved user can do. If they logout, they cannot log back in. This issue is patched in the `stable` version 2.7.13, `beta` version 2.8.0.beta11, and `tests-passed` version 2.8.0.beta11. One may disable invites as a workaround. Administrators can increase `min_trust_level_to_allow_invite` to reduce the attack surface to more trusted users.
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Analysis
by VulDB Data Team • 01/16/2022
The vulnerability described in CVE-2022-21684 affects Discourse, an open source discussion platform that serves as a collaborative forum system for communities and organizations. This security flaw represents a critical access control bypass issue that undermines the platform's user approval mechanisms and could potentially allow unauthorized individuals to gain elevated privileges within a community. The vulnerability specifically targets installations where the `must_approve_users` setting is enabled, which is designed to require administrator approval before new users can fully participate in the forum. The flaw exists in multiple release channels including stable, beta, and tests-passed versions, indicating a widespread impact across the platform's deployment scenarios.
The technical implementation of this vulnerability stems from a failure in the authentication flow logic when processing email invitations for new users. When a user receives an email invitation to join a Discourse community where the `must_approve_users` flag is enabled, the system should normally prevent these users from logging in until an administrator explicitly approves their account. However, the flaw allows these invited users to bypass this critical security check and automatically gain full login access to the community. This occurs during the initial login process when the system incorrectly grants access to unapproved users, treating them as if they had already been approved by an administrator. The bypass affects the core authentication and authorization mechanisms that should enforce trust levels and user approval workflows within the platform's access control model.
The operational impact of this vulnerability is significant as it creates a backdoor that allows potentially malicious actors to gain full administrative capabilities within a compromised Discourse community. Once logged in, unauthorized users can perform all actions that approved members can do, including posting content, moderating discussions, accessing private messages, and potentially modifying community settings. The vulnerability specifically affects users who are invited via email to communities with strict approval requirements, making it particularly dangerous for organizations that rely on these approval mechanisms to control community access. The security implications extend beyond simple unauthorized access as the compromised users could potentially use their elevated privileges to manipulate forum content, impersonate legitimate members, or conduct other malicious activities that would be difficult to trace. The fact that users cannot log back in after logging out provides only a partial mitigation, as the initial compromise still allows for immediate access to community resources.
The vulnerability is addressed through patches released in Discourse version 2.7.13 for the stable channel, and version 2.8.0.beta11 for both beta and tests-passed channels, indicating that the development team has recognized the severity of this access control bypass. Organizations can implement several mitigation strategies to address this vulnerability while awaiting updates or during the patch deployment process. The primary workaround involves disabling the email invitation functionality entirely, which prevents new users from being invited and subsequently bypassing the approval process. Additionally, administrators can increase the `min_trust_level_to_allow_invite` setting to ensure that only users with higher trust levels can be invited to the community, thereby reducing the potential attack surface. This approach aligns with security best practices that emphasize least privilege access and layered defense mechanisms. The vulnerability demonstrates the importance of proper access control implementation and the need for comprehensive testing of authentication flows, particularly in collaborative platforms where user access and privilege management are critical components of the security architecture.
This vulnerability maps to CWE-284 Access Control Bypass, which specifically addresses improper access control mechanisms that allow unauthorized access to resources or functionality. The issue also aligns with ATT&CK technique T1078 Valid Accounts, as it involves unauthorized access to legitimate user accounts through a bypass of the normal approval process. The flaw represents a classic case of insufficient authorization checks in a collaborative platform, where the system fails to properly validate user status before granting access to community resources. The vulnerability highlights the critical importance of proper authentication flow design and the necessity of robust access control validation mechanisms in multi-user systems where different trust levels and approval processes must be maintained. Organizations should review their Discourse installations and ensure that appropriate patches are applied immediately to prevent exploitation of this access control bypass vulnerability.