Mattermost: 736,893 Fingerprint Matches on Self-Hosted Collaboration

Mattermost, a self-hosted collaboration platform, has been found in 736,893 instances that are externally reachable according to ZoomEye's index. The platform offers channel-based communication, direct messaging, file sharing, and various integrations such as webhooks, slash commands, and bots. Organizations choose Mattermost for its control over data storage, but managing the platform presents several security concerns.

A fingerprint search for "Mattermost" on ZoomEye returned 736,893 matches, indicating that a significant number of self-hosted Mattermost servers are accessible from the internet. This discovery raises concerns about the security of these deployments, as the conversations and data exchanged within Mattermost could be exposed. Unlike database leaks, chat leaks are measured in terms of context, such as conversations, credentials shared, and files uploaded.

The exposure of Mattermost servers without proper security measures can lead to unintended consequences. Incoming and outgoing webhook URLs, as well as personal access tokens, act as credentials that can authenticate systems to channels. These credentials are often pasted into documentation, tickets, and scripts, increasing the risk of unauthorized access. Bots and personal access tokens also pose risks, as their permissions are usually broader than intended, and their inventory is rarely maintained.

To mitigate these risks, organizations should review the placement of their Mattermost deployments and ensure they are not externally accessible. Implementing TLS and using authenticated access paths instead of directly exposed ports can help secure the service. If external access is necessary for remote staff, it should be terminated at a component whose exposure has been reviewed.

It is essential to inventory webhooks, bots, and personal access tokens, rotate unnecessary credentials, and store the remaining values in a secure secret manager rather than leaving them in channel history.

Organizations should enforce multi-factor authentication, particularly for administrators, and review sign-in logs for unexpected locations. Keeping the server, plugins, and connectors updated with patches is also crucial. The integration surface, which includes webhooks, bots, and plugins, changes frequently and should be treated with heightened security measures.

While the chat content may be sensitive, it is essential to remember that any credential typed into a channel should be considered disclosed, even after the message is deleted.

In conclusion, the discovery of 736,893 externally reachable Mattermost instances highlights the importance of proper security measures in self-hosted collaboration platforms. By reviewing network placement, securing credentials, and implementing robust access controls, organizations can better protect their internal communication channels from potential security risks.