CVE-2025-44004 is a high-severity vulnerability identified in the Mattermost Confluence Plugin versions prior to 1.5.0. The core issue is a missing authentication check (CWE-306) for a critical function within the plugin. Specifically, the plugin fails to verify whether the user making an API call to create a channel subscription is authorized to perform this action on the Mattermost instance. This lack of authorization enforcement allows an unauthenticated attacker to create channel subscriptions arbitrarily by invoking the create channel subscription endpoint via API calls. The vulnerability has a CVSS 3.1 base score of 7.2, indicating a high level of risk. The vector metrics indicate that the attack can be performed remotely (AV:N), with low attack complexity (AC:L), no privileges required (PR:N), and no user interaction needed (UI:N). The scope is changed (S:C), meaning the vulnerability affects resources beyond the scope of the vulnerable component. The impact on confidentiality and integrity is low (C:L, I:L), with no impact on availability (A:N). Although no known exploits are currently reported in the wild, the vulnerability's characteristics make it a significant risk for organizations using the affected plugin versions. The Mattermost Confluence Plugin integrates Mattermost, an open-source collaboration platform, with Atlassian Confluence, enabling channel subscriptions to Confluence content. Exploiting this vulnerability could allow attackers to subscribe channels without permission, potentially leading to unauthorized information disclosure or manipulation of collaboration workflows.

For European organizations, this vulnerability poses a risk primarily to the confidentiality and integrity of internal communications and collaboration data. Unauthorized channel subscriptions could expose sensitive Confluence content to unintended audiences, increasing the risk of data leakage. Additionally, attackers could manipulate subscription settings to disrupt normal collaboration processes or gain footholds for further attacks within the Mattermost environment. Organizations in sectors with stringent data protection regulations, such as finance, healthcare, and government, could face compliance violations if sensitive information is exposed. The lack of authentication requirement and remote exploitability mean that attackers can attempt exploitation without prior access, increasing the threat surface. Given Mattermost's growing adoption in European enterprises as a secure communication tool, this vulnerability could affect a broad range of organizations, especially those integrating Mattermost with Confluence for knowledge management and collaboration.

To mitigate this vulnerability, European organizations should prioritize upgrading the Mattermost Confluence Plugin to version 1.5.0 or later, where the authentication checks are properly enforced. Until the patch is applied, organizations should consider restricting access to the Mattermost API endpoints by implementing network-level controls such as IP whitelisting and firewall rules to limit API access to trusted internal networks only. Additionally, monitoring API usage logs for unusual or unauthorized create channel subscription requests can help detect exploitation attempts early. Organizations should also review and tighten permissions and access controls within both Mattermost and Confluence to minimize the impact of any unauthorized subscriptions. Employing Web Application Firewalls (WAFs) with custom rules to detect and block suspicious API calls targeting the vulnerable endpoint can provide an additional layer of defense. Finally, educating administrators and users about the risks and signs of exploitation can improve incident response readiness.