On June 7, 2024, Mattermost—a popular open-source collaboration platform—received a critical security advisory: CVE-2025-24866. This vulnerability affects Mattermost versions 9.11.x up to 9.11.8, where insufficient access controls in the /api/v4/audits endpoint let some users view logs they shouldn't have access to.

This vulnerability bypasses compliance monitoring permissions and puts sensitive user activity data at risk. Here, I'll walk you step-by-step through the details, including what causes this bug, a realistic code snippet, and a working example exploit—explained in plain English.

Mattermost server versions 9.11. to 9.11.8 (inclusive)

- Any users with "delegated granular administration" roles who are NOT supposed to have Compliance Monitoring access

What’s the Problem?

Mattermost has many roles and permission levels. Some admins are given "delegated granular" rights; they can manage certain settings or users without accessing wider compliance features, like viewing all user activity logs.

However, in the vulnerable versions, the server fails to check if the current user really has permission to see the /api/v4/audits endpoint. That means admins with limited roles can simply call this endpoint and see activity logs for everyone—even if they're not allowed.

The Core Issue: Missing Permission Checks

Let's zoom in. In a secure setup, if someone tries to access user activity logs (audit logs), Mattermost should check if the user has the manage_system or compliance_monitoring_access roles. But in these versions, if you have a delegated granular admin role (e.g., you manage teams, but NOT audits), the endpoint still grants you access.

Code Snippet Example (Hypothetical, For Understanding)

// Old, Vulnerable Handler in Mattermost
func getAuditLogs(c *Context, w http.ResponseWriter, r *http.Request) {
    // Only this check – too broad!
    if !c.App.SessionHasPermissionTo(c.Session(), model.PermissionManageSystem) {
        c.SetPermissionError(model.PermissionManageSystem)
        return
    }
    // No compliance permission check!
    logs, _ := c.App.GetAuditLogs(...)
    // ...
    WriteResponse(w, r, logs)
}

The GetAuditLogs function just checks for manage_system, but it should also check for direct compliance monitoring rights!

Who Can Attack?

- Any user with a delegated admin role who has NO business seeing user audit logs—like a Team Admin or someone with a custom limited role.

`http

GET /api/v4/audits HTTP/1.1

Proof-of-Concept: Curl Command

curl -H "Authorization: Bearer YOUR_API_TOKEN" \
     https://mattermost.example.com/api/v4/audits

Insider threats: Non-compliance admins can harvest audit trails.

Essentially, your company’s compliance boundary can be silently bypassed by anyone with enough role privileges.

The Fix

Mattermost fixed this in 9.11.9 (and later versions).

Patch Strategy

Updated /api/v4/audits handler to enforce both manage_system AND compliance_monitoring_access checks.

// Patched Handler (simplified)
func getAuditLogs(c *Context, w http.ResponseWriter, r *http.Request) {
    if !c.App.SessionHasPermissionTo(c.Session(), model.PermissionManageSystem) ||
       !c.App.SessionHasPermissionTo(c.Session(), model.PermissionViewCompliance) {
        c.SetPermissionError(...)
        return
    }
    logs, _ := c.App.GetAuditLogs(...)
    WriteResponse(w, r, logs)
}

Mitigation: What Should You Do?

- Upgrade now: Mattermost 9.11.9 or later.

Monitor audit logs: Check for unusual access from delegated admins.

If you can’t upgrade, firewall off the /api/v4/audits endpoint or remove any non-essential delegated admin roles.

References

- Mattermost Security Advisory
- Mattermost Release Notes
- Official Mattermost Documentation – Roles

Conclusion

CVE-2025-24866 is a great example of why fine-grained access controls are crucial in any collaboration tool. Even "semi-admin" rights can go too far! If you use Mattermost, scan your version and upgrade straight away. Audit your admin groups, and stay alert for privilege escalation bugs in all your tools.

Timeline

Published on: 04/10/2025 16:15:27 UTC
Last modified on: 04/11/2025 15:39:52 UTC