CVE-2025-8402
📋 TL;DR
This vulnerability allows system administrators to crash Mattermost servers by importing malformed data through the bulk import feature. It affects Mattermost versions 10.8.x up to 10.8.3, 10.5.x up to 10.5.8, 9.11.x up to 9.11.17, 10.10.x up to 10.10.0, and 10.9.x up to 10.9.3. The issue stems from improper validation of import data (CWE-476: NULL Pointer Dereference).
💻 Affected Systems
- Mattermost
📦 What is this software?
Mattermost Server by Mattermost
Mattermost Server by Mattermost
Mattermost Server by Mattermost
Mattermost Server by Mattermost
Mattermost Server by Mattermost
⚠️ Risk & Real-World Impact
Worst Case
A malicious or compromised system administrator could cause persistent denial of service, disrupting team communication and collaboration until the server is manually restarted.
Likely Case
Accidental triggering by administrators performing legitimate bulk imports could cause temporary service disruption requiring manual intervention.
If Mitigated
With proper access controls limiting bulk import to trusted administrators only, impact is limited to potential accidental disruption.
🎯 Exploit Status
Exploitation requires system administrator privileges and knowledge of how to craft malicious import data.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Update to versions beyond those listed in affected versions (check Mattermost security updates for specific fixed versions)
Vendor Advisory: https://mattermost.com/security-updates
Restart Required: No
Instructions:
1. Check current Mattermost version. 2. Backup configuration and data. 3. Update to latest patched version following Mattermost upgrade documentation. 4. Verify functionality post-update.
🔧 Temporary Workarounds
Disable Bulk Import Feature
allTemporarily disable the bulk import functionality to prevent exploitation while planning patching.
Edit Mattermost config.json to set 'EnableBulkImport' to false
Restrict Administrator Access
allLimit system administrator roles to only essential personnel to reduce attack surface.
Review and audit system administrator accounts in Mattermost
🧯 If You Can't Patch
- Implement strict access controls to limit who can perform bulk imports
- Monitor server logs for bulk import attempts and server crashes
🔍 How to Verify
Check if Vulnerable:
Check Mattermost version via System Console > About or run 'mattermost version' command. Compare against affected version ranges.Check Version:
mattermost versionVerify Fix Applied:
After updating, verify version is beyond affected ranges and test bulk import functionality with valid data.📡 Detection & Monitoring
Log Indicators:
- Server crash logs following bulk import operations
- Error messages related to import data validation
Network Indicators:
- Unusual bulk import traffic patterns from administrator accounts
SIEM Query:
source="mattermost" AND ("bulk import" OR "import data") AND ("crash" OR "error" OR "failed")