CVE-2024-26145 in discourse-calendar
Summary
by MITRE • 02/21/2024
Discourse Calendar adds the ability to create a dynamic calendar in the first post of a topic on Discourse. Uninvited users are able to gain access to private events by crafting a request to update their attendance. This problem is resolved in commit dfc4fa15f340189f177a1d1ab2cc94ffed3c1190. As a workaround, one may use post visibility to limit access.
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Analysis
by VulDB Data Team • 02/06/2025
The vulnerability described in CVE-2024-26145 affects the Discourse Calendar plugin, which is designed to enable users to create dynamic calendars within Discourse forums. This feature allows users to schedule events and manage attendance within topic threads. The core issue stems from inadequate access controls that permit unauthorized users to manipulate event attendance data through crafted HTTP requests. The vulnerability specifically targets the calendar functionality's permission model, where private events should be restricted to authorized participants but can be accessed by uninvited users through direct API manipulation.
The technical flaw manifests in the calendar plugin's insufficient validation of user permissions when processing attendance update requests. When users attempt to modify their attendance status for events, the system fails to properly verify whether the requesting user has legitimate access rights to the specific event in question. This authorization bypass allows malicious actors to craft requests that update attendance records for private events they should not be able to access. The vulnerability operates at the application layer and leverages the plugin's API endpoints without proper authentication checks, making it particularly dangerous as it can be exploited through automated tools or manual request crafting.
The operational impact of this vulnerability extends beyond simple data exposure, as it fundamentally undermines the privacy and access control mechanisms of Discourse forums. Uninvited users can potentially gain unauthorized access to private event information, including event details, participant lists, and attendance records that should remain confidential. This breach of access control can lead to information disclosure, social engineering opportunities, and potential disruption of private discussions or sensitive planning activities within the forum environment. The vulnerability affects all instances using the affected Discourse Calendar plugin where private events are configured, making it a significant concern for organizations relying on Discourse for secure communications.
The fix implemented in commit dfc4fa15f340189f177a1d1ab2cc94ffed3c1190 addresses the core authorization issue by strengthening permission checks during attendance update operations. This fix ensures that each request to modify attendance status is properly validated against the user's access rights to the specific event. The workaround solution of using post visibility to limit access provides a temporary mitigation strategy that restricts who can see and interact with calendar-related content, though it does not address the underlying authorization flaw. Organizations should implement the official patch as soon as possible and consider additional monitoring of calendar-related API endpoints to detect potential exploitation attempts.
This vulnerability aligns with CWE-284, which describes improper access control issues in software systems. The flaw represents a classic authorization bypass where the system fails to properly verify user permissions before allowing sensitive operations. From an ATT&CK perspective, this vulnerability maps to T1078 legitimate credentials and T1566 credential access, as unauthorized users can gain access to private information through crafted requests that exploit the system's weak permission controls. The vulnerability demonstrates how web application plugins can introduce security gaps that compromise the overall security posture of the platform, emphasizing the importance of proper access control implementation in all application components.
Organizations using Discourse should conduct thorough security assessments of their calendar plugin configurations and review access control policies to ensure that private events remain properly protected. The vulnerability highlights the critical importance of implementing defense-in-depth strategies where multiple layers of security controls work together to prevent unauthorized access. Regular security audits of third-party plugins and components are essential to identify and remediate similar access control weaknesses that could potentially be exploited by malicious actors. The incident serves as a reminder that even seemingly benign features like calendar functionality can introduce significant security risks when proper access controls are not implemented.