CVE-2022-39385 in Discourse
Summary
by MITRE • 11/15/2022
Discourse is the an open source discussion platform. In some rare cases users redeeming an invitation can be added as a participant to several private message topics that they should not be added to. They are not notified of this, it happens transparently in the background. This issue has been resolved in commit `a414520742` and will be included in future releases. Users are advised to upgrade. Users are also advised to set `SiteSetting.max_invites_per_day` to 0 until the patch is installed.
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Analysis
by VulDB Data Team • 11/15/2022
The vulnerability identified as CVE-2022-39385 affects Discourse, an open source discussion platform designed for community engagement and collaboration. This security flaw represents a privilege escalation issue within the platform's invitation and private messaging systems, where users can potentially gain unauthorized access to private message topics through the redemption process. The vulnerability specifically manifests when users redeem invitations to join the platform, creating a scenario where they may be automatically added to multiple private message conversations without their knowledge or explicit consent. This transparent background operation occurs without any user notification or awareness, creating a significant security concern for organizations relying on Discourse for sensitive communications.
The technical root cause of this vulnerability lies in the platform's invitation redemption mechanism and its handling of private message topic assignments. When users redeem invitations, the system processes their addition to private message topics based on certain criteria that may inadvertently include users in multiple conversations they should not have access to. This flaw stems from inadequate access control validation during the automatic assignment process, allowing unauthorized participants to be silently included in private communications. The vulnerability is classified under CWE-284 Access Control, specifically representing insufficient access control in the context of user privilege management and resource access. The issue demonstrates poor input validation and insufficient authorization checks, as the system fails to properly verify user permissions before adding participants to private message topics during invitation redemption.
The operational impact of this vulnerability extends beyond simple privacy concerns to potentially compromise sensitive information within Discourse environments. Organizations using Discourse for internal communications, customer support, or collaborative projects may experience unauthorized access to confidential discussions, potentially leading to data breaches or information disclosure. The transparent nature of the vulnerability means that affected organizations may remain unaware of the unauthorized access until a security audit or incident investigation occurs. This issue particularly affects environments where Discourse serves as a primary communication platform for sensitive business operations, customer interactions, or collaborative projects requiring strict access controls. The vulnerability can be exploited by malicious actors who obtain invitation links or by users who may exploit the system to gain access to conversations they should not normally participate in, creating potential risks for organizations with strict data governance policies.
Mitigation strategies for this vulnerability involve immediate action from system administrators to implement the recommended security measures. The primary remediation approach requires upgrading to a patched version of Discourse that includes the fix committed as a414520742, which addresses the underlying access control flaw in the invitation redemption and private message assignment processes. In addition to the mandatory upgrade, administrators should configure the SiteSetting.max_invites_per_day parameter to zero as a temporary protective measure until the patch is fully implemented. This setting prevents additional invitation redemptions and provides a safeguard against further exploitation of the vulnerability during the transition period. Organizations should also conduct comprehensive security audits of their Discourse installations to identify any potential unauthorized access that may have occurred prior to patching. The mitigation approach aligns with ATT&CK technique T1078 Valid Accounts, as it addresses unauthorized access through legitimate user account mechanisms, and follows the principle of least privilege by restricting invitation redemption capabilities until the system is properly secured. Security teams should also monitor their systems for any unusual activity patterns that might indicate exploitation attempts and implement proper access logging to track user participation in private message topics.