CVE-2025-9078
📋 TL;DR
This vulnerability allows authenticated Mattermost users to access unauthorized posts and manipulate link previews through hash collision attacks on FNV-1 hashing. 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 10.10.1, and 10.9.x up to 10.9.3. Attackers must have valid user credentials to exploit this issue.
💻 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
Authenticated attackers could access sensitive posts they shouldn't have permission to view, potentially exposing confidential information, and could poison link previews to spread misinformation or malicious links.
Likely Case
Limited information disclosure where authenticated users access posts from channels they shouldn't have access to, and manipulation of link preview metadata.
If Mitigated
Minimal impact with proper access controls, monitoring, and network segmentation in place.
🎯 Exploit Status
Exploitation requires authenticated access and understanding of hash collision techniques against FNV-1 hashing.
🛠️ 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. Download and install patched version from official Mattermost releases. 4. Verify installation and functionality.
🔧 Temporary Workarounds
Disable Link Previews
allTemporarily disable link preview functionality to prevent hash collision attacks on link metadata
Set 'EnableLinkPreviews' to 'false' in config.json
🧯 If You Can't Patch
- Implement strict access controls and monitor for unusual post access patterns
- Segment Mattermost instance from sensitive networks and implement network monitoring
🔍 How to Verify
Check if Vulnerable:
Check Mattermost version against affected version ranges in System Console > AboutCheck Version:
Check System Console > About in Mattermost web interface or review server logsVerify Fix Applied:
Verify version is updated beyond affected ranges and test link preview functionality📡 Detection & Monitoring
Log Indicators:
- Unusual patterns of post access from authenticated users
- Multiple failed hash validations in server logs
Network Indicators:
- Unusual API calls to post metadata endpoints
- Suspicious patterns in link preview requests
SIEM Query:
source="mattermost" AND ("unauthorized post access" OR "hash validation failed" OR "cache key collision")