CVE-2025-53910 is a security vulnerability identified in the Mattermost Confluence Plugin versions prior to 1.5.0. The vulnerability is categorized under CWE-862, which refers to missing authorization. Specifically, the plugin fails to verify whether a user has the necessary access rights to a Mattermost channel before allowing the creation of a channel subscription via the plugin's API. This means an attacker can exploit the edit channel subscription API endpoint to create subscriptions to channels they do not have permission to access. The vulnerability does not require user interaction or authentication, and it can be exploited remotely over the network. The CVSS 3.1 base score is 4.0 (medium severity), with the vector indicating network attack vector (AV:N), high attack complexity (AC:H), no privileges required (PR:N), no user interaction (UI:N), scope changed (S:C), no confidentiality impact (C:N), low integrity impact (I:L), and no availability impact (A:N). The scope change indicates that the vulnerability affects resources beyond the initially vulnerable component, potentially impacting other components or data. Although the integrity impact is low, unauthorized channel subscription creation could lead to unauthorized data access or information leakage through channel notifications or message subscriptions. No known exploits are reported in the wild yet, and no patches are currently linked, indicating that organizations using affected versions should prioritize updates once available. The vulnerability arises from insufficient authorization checks in the plugin's API, which is a critical security oversight in access control mechanisms.

For European organizations using Mattermost with the Confluence Plugin, this vulnerability could lead to unauthorized access to channel subscriptions, potentially exposing sensitive internal communications or project information. While the vulnerability does not directly compromise confidentiality, the ability to subscribe to channels without proper authorization could allow attackers to receive updates or notifications intended only for authorized users, indirectly leading to information leakage. This could be particularly impactful in sectors with strict data privacy regulations such as finance, healthcare, and government institutions across Europe. The integrity impact is low but still relevant, as unauthorized subscriptions could be used to manipulate or monitor communication flows. Given the network-based exploitation and no requirement for authentication, attackers could remotely exploit this vulnerability, increasing the risk of widespread abuse. The medium severity rating suggests that while the vulnerability is not critical, it poses a tangible risk that should not be ignored, especially in environments where Mattermost is used for sensitive collaboration. The lack of known exploits in the wild provides a window of opportunity for organizations to remediate before active exploitation occurs.

European organizations should immediately assess their Mattermost Confluence Plugin versions and plan to upgrade to version 1.5.0 or later once available, as this version addresses the missing authorization checks. Until a patch is released, organizations can mitigate risk by restricting network access to the Mattermost API endpoints, especially the edit channel subscription API, using firewalls or API gateways to limit exposure. Implementing strict monitoring and logging of API calls related to channel subscriptions can help detect anomalous or unauthorized subscription creation attempts. Additionally, organizations should review and tighten access control policies within Mattermost and Confluence integrations, ensuring that only trusted users and systems have API access. Employing network segmentation to isolate Mattermost servers and enforcing multi-factor authentication for administrative access can further reduce risk. Finally, organizations should stay informed about updates from Mattermost and apply security patches promptly once released.