CVE-2025-6465
📋 TL;DR
This vulnerability allows authenticated users with file upload permissions to overwrite file attachment thumbnails via path traversal in Mattermost's file streaming APIs. Attackers could potentially replace legitimate thumbnails with malicious content. Affected systems include Mattermost versions 10.8.x up to 10.8.3, 10.5.x up to 10.5.8, 10.10.x up to 10.10.0, and 10.9.x up to 10.9.3.
💻 Affected Systems
- Mattermost
📦 What is this software?
Mattermost Server by Mattermost
Mattermost Server by Mattermost
Mattermost Server by Mattermost
Mattermost Server by Mattermost
⚠️ Risk & Real-World Impact
Worst Case
An attacker could replace legitimate file thumbnails with malicious content, potentially leading to phishing attacks, malware distribution, or defacement of the Mattermost interface.
Likely Case
Limited impact where attackers replace thumbnails with inappropriate or misleading content, causing confusion or minor disruption.
If Mitigated
Minimal impact if proper access controls and monitoring are in place, with only authenticated users able to exploit and limited to thumbnail manipulation.
🎯 Exploit Status
Exploitation requires authenticated access with file upload permissions and knowledge of the vulnerable API endpoints.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Upgrade to Mattermost versions 10.8.4, 10.5.9, 10.10.1, or 10.9.4
Vendor Advisory: https://mattermost.com/security-updates
Restart Required: No
Instructions:
1. Backup your Mattermost configuration and database. 2. Download the patched version from the official Mattermost website. 3. Follow the Mattermost upgrade documentation for your deployment type. 4. Verify the upgrade completed successfully.
🔧 Temporary Workarounds
Restrict file upload permissions
allTemporarily limit file upload capabilities to only essential users until patching can be completed.
Use Mattermost System Console > Permissions to adjust file upload settings
Implement file upload monitoring
allEnable detailed logging for file upload activities and monitor for suspicious patterns.
Configure Mattermost logging to capture file upload events at DEBUG level
🧯 If You Can't Patch
- Implement strict access controls to limit file upload permissions to trusted users only
- Deploy WAF rules to detect and block path traversal attempts in API requests
🔍 How to Verify
Check if Vulnerable:
Check your Mattermost version via System Console > About Mattermost. If version matches affected ranges, you are vulnerable.Check Version:
For command line: `mattermost version` or check System Console > About Mattermost in web interfaceVerify Fix Applied:
After upgrading, verify the version shows as patched (10.8.4, 10.5.9, 10.10.1, or 10.9.4) in System Console > About Mattermost.📡 Detection & Monitoring
Log Indicators:
- Unusual file upload patterns
- API requests with path traversal sequences (../)
- Multiple thumbnail modification attempts from single user
Network Indicators:
- Unusual spikes in file upload API traffic
- Requests to file streaming endpoints with malformed parameters
SIEM Query:
source="mattermost" AND (message="*file upload*" OR message="*thumbnail*" OR message="*../*")