CVE-2025-41423 is an authorization vulnerability affecting Mattermost versions 9.11.x up to 9.11.10, 10.4.x up to 10.4.2, and 10.5.x up to 10.5.0. The flaw resides in the API endpoint /plugins/playbooks/api/v0/signal/keywords/ignore-thread, which is part of the Playbooks plugin functionality. This endpoint is intended to allow authorized users to manage threads related to Playbooks bot actions, specifically to ignore certain keywords or threads. However, due to improper permission validation (CWE-863: Incorrect Authorization), any user or attacker can invoke this API to delete posts created by the Playbooks bot, even if they lack channel access or the necessary permissions. This bypass of authorization controls means that unauthorized users can manipulate or remove critical workflow or operational messages generated by the Playbooks bot, potentially disrupting communication and automated processes within Mattermost channels. The vulnerability does not require channel membership or elevated privileges, and no user interaction beyond sending the API request is necessary. Although no known exploits have been reported in the wild, the vulnerability presents a risk of unauthorized content deletion, which could be leveraged to interfere with incident response, operational coordination, or audit trails maintained via Playbooks. The lack of a patch link suggests that a fix may not yet be publicly available or is pending release. The vulnerability was reserved and published in April 2025, with enrichment from CISA indicating recognition by US cybersecurity authorities.

For European organizations using Mattermost, especially those leveraging the Playbooks plugin for operational workflows, this vulnerability could lead to unauthorized deletion of critical posts. This undermines the integrity and availability of communication and automated task tracking within teams, potentially causing confusion, loss of audit trails, and disruption of coordinated responses to incidents or projects. Organizations in sectors such as finance, healthcare, government, and critical infrastructure that rely on Mattermost for secure internal communication and incident management could face operational risks. The ability for any user, including potentially external or low-privileged insiders, to delete posts without proper authorization increases the attack surface for insider threats or opportunistic attackers. While confidentiality is less directly impacted, the integrity and availability of key operational data are at risk. This could delay response times, cause miscommunication, or result in loss of evidence needed for compliance or forensic investigations. The medium severity rating reflects the moderate impact and the fact that exploitation does not require complex conditions, but the scope is limited to Mattermost instances running the affected versions with the Playbooks plugin enabled.

1. Immediate mitigation should include restricting access to Mattermost instances to trusted users only, enforcing strong authentication and monitoring for unusual API usage patterns targeting the /plugins/playbooks/api/v0/signal/keywords/ignore-thread endpoint. 2. Disable or remove the Playbooks plugin temporarily if it is not critical to operations until a patch is available. 3. Implement network-level controls such as Web Application Firewalls (WAFs) to detect and block unauthorized API calls targeting this endpoint. 4. Monitor Mattermost logs for unexpected deletions of posts, especially those generated by the Playbooks bot, to detect potential exploitation attempts. 5. Engage with Mattermost support or vendor channels to obtain and apply patches or updates as soon as they are released. 6. Educate users and administrators about the risk and encourage prompt reporting of suspicious activity. 7. Consider implementing additional internal logging or backup mechanisms for critical Playbooks posts to enable recovery if deletion occurs. 8. Review and tighten role-based access controls and API permissions within Mattermost to minimize exposure.