CVE-2025-54458 is a medium severity vulnerability identified in the Mattermost Confluence Plugin versions prior to 1.5.0. The core issue is a missing authorization check (CWE-862) in the plugin's create subscription endpoint. Specifically, the plugin fails to verify whether a user has access rights to a given Confluence space before allowing them to create a subscription for that space. This means an attacker with at least limited privileges (low privileges, requiring authentication) can create subscriptions to Confluence spaces they are not authorized to access. The vulnerability does not allow direct data disclosure or modification (confidentiality impact is limited), nor does it affect data integrity or availability directly. However, by subscribing to unauthorized spaces, an attacker may receive notifications or updates about content changes in those spaces, potentially leading to information leakage. The CVSS 3.1 score is 5.0 (medium), reflecting network attack vector, low attack complexity, requiring privileges but no user interaction, and limited confidentiality impact. No known exploits are reported in the wild yet, and no patches are currently linked, indicating that organizations should prioritize updating once a patch is available. The vulnerability affects the Mattermost Confluence Plugin, which integrates Mattermost messaging with Atlassian Confluence collaboration spaces, commonly used in enterprise environments for team communication and documentation.

For European organizations, this vulnerability could lead to unauthorized access to internal collaboration content via subscription notifications, potentially exposing sensitive project information, strategic plans, or personal data shared within Confluence spaces. While it does not allow direct content modification or deletion, the leakage of information through subscription notifications can violate data protection regulations such as GDPR if personal or confidential data is involved. Organizations in sectors with strict compliance requirements (finance, healthcare, government) are particularly at risk. Additionally, the breach of internal collaboration confidentiality could aid further social engineering or targeted attacks. Since Mattermost and Confluence are widely used in European enterprises for internal communication and documentation, the impact is significant especially in organizations that have integrated these platforms without strict access controls or monitoring. The medium severity rating suggests that while the risk is not critical, it should not be ignored, especially in environments with sensitive data.

1. Immediate mitigation involves restricting access to the Mattermost Confluence Plugin's subscription features to trusted users only, minimizing the number of users with privileges to create subscriptions. 2. Implement strict role-based access controls (RBAC) within Mattermost and Confluence to ensure users only have permissions necessary for their roles. 3. Monitor subscription creation logs and audit trails for unusual subscription activities, especially subscriptions to spaces outside a user's normal access scope. 4. Until a patch is released, consider disabling the Confluence plugin or the subscription creation endpoint if feasible to prevent exploitation. 5. Educate users and administrators about the vulnerability and encourage vigilance regarding unexpected notifications or subscription changes. 6. Once available, promptly apply vendor patches or updates that address the authorization check flaw. 7. Review and tighten integration configurations between Mattermost and Confluence to ensure proper authentication and authorization enforcement. 8. Employ network segmentation and monitoring to detect anomalous access patterns related to the plugin's API endpoints.