CVE-2025-20033
📋 TL;DR
This vulnerability in Mattermost allows attackers to create denial-of-service conditions by exploiting improper validation of post types. Attackers with sysconsole_read_plugins permission can create posts with custom_pl_notification type and specific props, disrupting service for affected users. This affects Mattermost instances running vulnerable versions.
💻 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
Complete denial of service for users with sysconsole_read_plugins permission, disrupting collaboration and communication within the Mattermost instance.
Likely Case
Temporary service disruption for users with sysconsole_read_plugins permission until the malicious post is removed or the system is restarted.
If Mitigated
Minimal impact if proper access controls limit sysconsole_read_plugins permission to trusted administrators only.
🎯 Exploit Status
Exploitation requires authenticated access with specific permission. No public exploit code has been disclosed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Update to Mattermost 10.2.1, 9.11.6, 10.0.4, or 10.1.4
Vendor Advisory: https://mattermost.com/security-updates
Restart Required: Yes
Instructions:
1. Backup your Mattermost instance and database. 2. Download the patched version from Mattermost releases. 3. Stop the Mattermost service. 4. Install the patched version. 5. Restart the Mattermost service. 6. Verify the update was successful.
🔧 Temporary Workarounds
Restrict sysconsole_read_plugins permission
allTemporarily remove sysconsole_read_plugins permission from non-essential users until patching can be completed.
Use Mattermost System Console to modify role permissions
🧯 If You Can't Patch
- Review and restrict sysconsole_read_plugins permission to only essential administrators
- Implement monitoring for posts with custom_pl_notification type and alert on suspicious activity
🔍 How to Verify
Check if Vulnerable:
Check Mattermost version via System Console > About Mattermost or run: mattermost versionCheck Version:
mattermost versionVerify Fix Applied:
Verify version is 10.2.1, 9.11.6, 10.0.4, or 10.1.4 or higher📡 Detection & Monitoring
Log Indicators:
- Posts created with custom_pl_notification type
- Multiple failed service requests from users with sysconsole_read_plugins permission
Network Indicators:
- Increased error responses from Mattermost API endpoints
SIEM Query:
source="mattermost" AND ("custom_pl_notification" OR "sysconsole_read_plugins")