CVE-2022-41913 is a medium-severity vulnerability classified under CWE-200, which pertains to the exposure of sensitive information to unauthorized actors. This vulnerability affects the discourse-calendar plugin for the Discourse messaging platform, specifically versions prior to 0.3. The discourse-calendar plugin enables users to create dynamic calendars within the first post of a topic, allowing event creation and editing capabilities. The vulnerability arises in environments where the discourse post events feature is enabled. In such configurations, unauthorized users can list members of private groups or public groups that contain private members, thereby exposing sensitive membership information that should otherwise remain confidential. This exposure can occur because the plugin does not adequately restrict access to group membership data when post events are enabled. The issue does not require exploitation through complex attack vectors; rather, it leverages the existing functionality of the plugin to access information that should be restricted. The vulnerability has been addressed in commit ca5ae3e7e, which will be included in future releases of the plugin. Until users can upgrade, mitigation can be achieved by disabling the discourse_post_event_enabled setting, which fully prevents the vulnerability from being exploited. Alternatively, administrators can remove all groups from the discourse_post_event_allowed_on_groups setting to prevent regular users from exploiting the vulnerability, though moderators will retain the ability to use the feature and potentially access the sensitive information. There are no known exploits in the wild at this time, and the vulnerability requires that the discourse post events feature be enabled, limiting the scope of affected systems to those configured with this feature active.

For European organizations using the Discourse platform with the discourse-calendar plugin enabled and post events activated, this vulnerability poses a risk of unauthorized disclosure of private group membership information. Such exposure can lead to privacy violations, reputational damage, and potential facilitation of targeted social engineering or phishing attacks by revealing organizational structures or sensitive group affiliations. Confidentiality is primarily impacted, as unauthorized actors can access information meant to be restricted. The integrity and availability of systems are not directly affected by this vulnerability. Organizations handling sensitive or regulated data, such as those in finance, healthcare, or government sectors, may face compliance risks under GDPR and other privacy regulations if private membership data is exposed. The limited scope—only sites with post events enabled—and the absence of known active exploitation reduce the immediate threat level but do not eliminate the risk, especially in environments with high-value or sensitive group memberships.

To mitigate this vulnerability effectively, European organizations should prioritize upgrading the discourse-calendar plugin to version 0.3 or later, which includes the patch for CVE-2022-41913. If immediate upgrading is not feasible, administrators should disable the discourse_post_event_enabled setting to fully prevent exploitation. As an interim measure, removing all groups from the discourse_post_event_allowed_on_groups setting can restrict regular users from exploiting the vulnerability, though this does not prevent moderators from accessing the sensitive information. Organizations should audit their Discourse configurations to identify if the post events feature is enabled and assess the sensitivity of group membership data exposed via the plugin. Additionally, monitoring access logs for unusual activity related to group membership queries can help detect potential exploitation attempts. Implementing strict access controls and limiting moderator privileges to trusted personnel will further reduce risk. Finally, organizations should review their privacy policies and user agreements to ensure compliance with data protection regulations in light of this vulnerability.