CVE-2025-9079: Mattermost Server RCE Vulnerability

CVE-2025-9079 Overview

CVE-2025-9079 affects multiple versions of Mattermost Server. The vulnerability allows administrator-level users to execute arbitrary code by uploading a malicious plugin to the prepackaged plugins directory. The flaw stems from improper validation of the import directory path configuration, classified as [CWE-22] Path Traversal.

Affected releases include Mattermost 10.8.x <= 10.8.3, 10.5.x <= 10.5.8, 9.11.x <= 9.11.17, 10.10.x <= 10.10.1, and 10.9.x <= 10.9.3. An authenticated administrator can leverage the missing path validation to drop a crafted plugin that the server executes during processing.

Critical Impact
Authenticated administrators can achieve arbitrary code execution on the Mattermost server, compromising confidentiality, integrity, and availability of the host system.

Affected Products

Mattermost Server 10.8.x through 10.8.3
Mattermost Server 10.5.x through 10.5.8, 10.9.x through 10.9.3, 10.10.x through 10.10.1
Mattermost Server 9.11.x through 9.11.17

Discovery Timeline

2025-09-19 - CVE-2025-9079 published to NVD
2025-09-25 - Last updated in NVD database

Technical Details for CVE-2025-9079

Vulnerability Analysis

The vulnerability resides in Mattermost Server's handling of the import directory path configuration. The server fails to validate the configured path before processing plugin files placed in the prepackaged plugins directory. An administrator can manipulate the configuration so that attacker-controlled plugin artifacts are loaded and executed by the server process.

Because Mattermost plugins run server-side with the privileges of the Mattermost service, successful exploitation yields code execution under that service account. This enables credential theft, data exfiltration from the messaging platform, lateral movement, and persistence on the host. The classification under [CWE-22] reflects the path-handling weakness that permits a writable location to be treated as a trusted plugin source.

Root Cause

Mattermost Server does not enforce constraints on the import directory path used to stage plugin files. The application accepts a configured path without verifying that it resides within an expected, restricted location. Files copied or uploaded into this path are subsequently treated as prepackaged plugins and loaded by the server.

Attack Vector

Exploitation requires a network-reachable Mattermost instance and valid administrator credentials. The attacker modifies the import directory configuration or places a crafted plugin into the resolved directory. When Mattermost processes the prepackaged plugins, the malicious binary or script executes within the server context.

No public proof-of-concept code is available for this issue. Refer to the Mattermost Security Updates advisory for vendor technical details.

Detection Methods for CVE-2025-9079

Indicators of Compromise

Unexpected files appearing in the Mattermost prepackaged_plugins directory outside of vendor releases
Modifications to the ImportDirectory setting in config.json pointing to unusual paths
Child processes spawned by the Mattermost server binary that do not match known plugin behavior
Outbound network connections from the Mattermost service to unfamiliar hosts following a plugin upload event

Detection Strategies

Audit Mattermost administrator activity logs for changes to plugin configuration, file uploads, and import directory settings
Monitor file integrity on the Mattermost installation directory, particularly the plugins and prepackaged plugins folders
Alert on new plugin manifests (plugin.json) that are not signed by Mattermost or an approved publisher

Monitoring Recommendations

Forward Mattermost audit and system logs to a centralized analytics platform for correlation with host telemetry
Track process lineage from the Mattermost server binary to identify unexpected child executions
Review administrator account usage patterns and enforce alerts on privilege configuration changes

How to Mitigate CVE-2025-9079

Immediate Actions Required

Upgrade Mattermost Server to a fixed release as listed in the Mattermost Security Updates advisory
Review and restrict the set of accounts holding system administrator privileges within Mattermost
Audit the current ImportDirectory configuration and reset it to a path under tight filesystem permissions
Inspect the prepackaged plugins directory for unauthorized files and remove any not provided by Mattermost

Patch Information

Mattermost has released fixed versions addressing CVE-2025-9079. Administrators should upgrade beyond 10.8.3, 10.5.8, 9.11.17, 10.10.1, and 10.9.3. Patch details are published at the Mattermost Security Updates portal.

Workarounds

Restrict filesystem permissions on the Mattermost plugin and import directories so only the service account can write
Enforce multi-factor authentication on all Mattermost administrator accounts to reduce abuse of privileged sessions
Disable plugin uploads in environments where they are not required by setting PluginSettings.EnableUploads to false
Apply application allowlisting on the Mattermost host to block execution of unsigned plugin binaries

bash

# Configuration example: harden plugin upload settings in config.json
{
  "PluginSettings": {
    "Enable": true,
    "EnableUploads": false,
    "AutomaticPrepackagedPlugins": false,
    "Directory": "/opt/mattermost/plugins",
    "ClientDirectory": "/opt/mattermost/client/plugins"
  }
}