CVE-2025-25279: Mattermost Server Path Traversal Flaw

CVE-2025-25279 Overview

CVE-2025-25279 is a path traversal vulnerability in Mattermost Server's Boards feature that allows unauthenticated attackers to read arbitrary files from the underlying system. The vulnerability stems from improper validation of board blocks during the import process, enabling attackers to craft malicious import archives that can exfiltrate sensitive system files when processed by the server.

Critical Impact
Unauthenticated attackers can read sensitive files including configuration files, credentials, and private keys from Mattermost servers by exploiting the Boards import/export functionality.

Affected Products

Mattermost Server versions 10.4.x through 10.4.1
Mattermost Server versions 10.3.x through 10.3.2
Mattermost Server versions 10.2.x through 10.2.2
Mattermost Server versions 9.11.x through 9.11.7

Discovery Timeline

2025-02-24 - CVE-2025-25279 published to NVD
2025-10-02 - Last updated in NVD database

Technical Details for CVE-2025-25279

Vulnerability Analysis

This vulnerability is classified as CWE-22 (Improper Limitation of a Pathname to a Restricted Directory), commonly known as path traversal or directory traversal. The flaw exists in the Mattermost Boards feature, specifically in how the application processes imported board archives.

When users import boards into Mattermost, the server processes the archive contents and extracts board blocks including any referenced files. The vulnerability arises because the import functionality fails to properly sanitize file paths within the imported archive. An attacker can craft a malicious archive containing specially constructed path references using directory traversal sequences (such as ../) that escape the intended directory boundaries.

Upon successful exploitation, the attacker gains read access to arbitrary files on the server filesystem with the permissions of the Mattermost service account. This can expose critical system files, application configuration files containing database credentials, API keys, and other sensitive data.

Root Cause

The root cause is insufficient input validation in the board block import handler. When processing imported board archives, the application does not adequately validate or sanitize file path references within board blocks before accessing the filesystem. This allows path traversal sequences to be processed, enabling attackers to reference files outside the intended import directory.

Attack Vector

The attack is network-based and requires no authentication or user interaction. An attacker exploits this vulnerability by:

Creating a malicious board archive containing board blocks with path traversal sequences pointing to target files (e.g., /etc/passwd, configuration files, private keys)
Importing the crafted archive into a Mattermost instance via the Boards import functionality
Exporting the imported board, which triggers the server to read and include the targeted arbitrary files
Extracting the sensitive file contents from the exported archive

The attack leverages the legitimate import/export functionality of Mattermost Boards, making it difficult to distinguish from normal operations without specific validation controls.

Detection Methods for CVE-2025-25279

Indicators of Compromise

Unusual file access patterns in server logs showing reads of sensitive system files like /etc/passwd, /etc/shadow, or application configuration files
Board import operations containing path traversal sequences (../, ..%2f, %2e%2e/) in file references
Anomalous export requests following recent import operations, particularly from unknown or suspicious sources
Unexpected access to files outside the Mattermost data directory by the Mattermost service process

Detection Strategies

Monitor Mattermost application logs for board import and export operations, correlating them with file access events
Implement file integrity monitoring (FIM) on sensitive configuration files and system directories
Deploy network-based detection rules to identify board archives containing path traversal patterns
Enable audit logging on the Mattermost data directory and monitor for access attempts outside expected paths

Monitoring Recommendations

Configure SentinelOne to monitor the Mattermost service process for file access operations outside the application data directory
Set up alerts for any read operations on sensitive files (/etc/passwd, config.json, private key files) by the Mattermost process
Implement log aggregation to correlate board import events with subsequent file system activity
Monitor for high-frequency import/export operations which may indicate exploitation attempts

How to Mitigate CVE-2025-25279

Immediate Actions Required

Upgrade Mattermost Server immediately to a patched version: 10.4.2+, 10.3.3+, 10.2.3+, or 9.11.8+
If immediate patching is not possible, consider temporarily disabling the Boards plugin or restricting board import functionality
Audit recent board import and export activity logs for signs of exploitation
Review server file access logs for any unauthorized file reads

Patch Information

Mattermost has released security updates addressing this vulnerability. Refer to the Mattermost Security Updates page for the latest patched versions and detailed upgrade instructions. Organizations should prioritize this update given the unauthenticated nature of the attack and the potential for sensitive data exfiltration.

Workarounds

Restrict network access to Mattermost Boards import functionality using firewall rules or reverse proxy configurations
Disable the Boards plugin entirely if not required for business operations until patching is complete
Implement Web Application Firewall (WAF) rules to block requests containing path traversal sequences in board import payloads
Run the Mattermost service under a restricted user account with minimal filesystem permissions to limit exposure

bash

# Disable Mattermost Boards plugin via CLI
sudo -u mattermost /opt/mattermost/bin/mattermost plugin disable focalboard

# Alternatively, restrict Boards feature in config.json
# Set "EnablePublicSharedBoards": false and "EnableBoardsFeatureFlags": false