CVE-2025-44001 is a security vulnerability identified in the Mattermost Confluence Plugin versions prior to 1.5.0. The vulnerability is classified under CWE-862, which refers to Missing Authorization. Specifically, the plugin fails to verify whether a user has the appropriate access rights to a Mattermost channel before allowing an API call to retrieve channel subscription details. This flaw allows an unauthenticated attacker to query the Get Channel Subscriptions details endpoint and obtain information about channel subscribers without proper authorization. The vulnerability does not require user interaction or authentication, making it remotely exploitable over the network. The CVSS v3.1 base score is 4.0 (medium severity), reflecting that the attack vector is network-based (AV:N), requires high attack complexity (AC:H), no privileges (PR:N), no user interaction (UI:N), and impacts confidentiality only (C:L), without affecting integrity or availability. The scope is changed (S:C), indicating that the vulnerability affects resources beyond the security scope of the vulnerable component. Although no known exploits are currently reported in the wild, the vulnerability could be leveraged to gather sensitive information about channel subscriptions, potentially aiding further targeted attacks or reconnaissance. The lack of a patch link suggests that a fix may not yet be publicly available or is pending release. Organizations using Mattermost with the Confluence Plugin should prioritize upgrading to version 1.5.0 or later once available or apply compensating controls to restrict access to the vulnerable API endpoint.

For European organizations, this vulnerability poses a risk primarily to confidentiality. Unauthorized disclosure of channel subscription details could reveal sensitive information about internal communication groups, membership, and collaboration patterns. This information could be exploited by threat actors for social engineering, targeted phishing, or lateral movement within the network. While the vulnerability does not directly compromise data integrity or availability, the exposure of subscription metadata could undermine operational security and privacy compliance, especially under GDPR regulations. Organizations in sectors with strict data protection requirements, such as finance, healthcare, and government, may face increased reputational and regulatory risks if such information is leaked. The medium severity score reflects that the impact is limited to information disclosure without direct system compromise, but the ease of remote exploitation without authentication increases the urgency to address this issue.

1. Upgrade the Mattermost Confluence Plugin to version 1.5.0 or later as soon as the patch is released to ensure proper authorization checks are enforced. 2. Until a patch is available, restrict network access to the vulnerable API endpoint by implementing firewall rules or API gateway policies that limit calls to trusted users or IP ranges. 3. Monitor API usage logs for unusual or unauthorized access patterns to the Get Channel Subscriptions endpoint to detect potential exploitation attempts. 4. Conduct an internal audit of channel subscription data exposure and review access controls on Mattermost channels to minimize sensitive information leakage. 5. Educate administrators and users about the risks of unauthorized information disclosure and encourage prompt reporting of suspicious activities. 6. Consider deploying Web Application Firewalls (WAF) with custom rules to block unauthorized API calls targeting this endpoint. 7. Coordinate with Mattermost support or vendor channels to obtain timely updates and security advisories related to this vulnerability.