CVE-2025-14822
📋 TL;DR
Mattermost versions 10.11.0 through 10.11.8 have a CPU exhaustion vulnerability where authenticated users can send posts with thousands of space-separated tokens that aren't properly validated before hashtag processing. This allows attackers to cause denial of service by consuming excessive CPU resources. Only authenticated users can exploit this vulnerability.
💻 Affected Systems
- Mattermost
📦 What is this software?
Mattermost Server by Mattermost
⚠️ Risk & Real-World Impact
Worst Case
Complete service unavailability due to CPU exhaustion, affecting all users of the Mattermost instance until the malicious request completes or the service is restarted.
Likely Case
Temporary performance degradation or service slowdown affecting user experience, potentially requiring administrator intervention to identify and block the malicious user.
If Mitigated
Minimal impact with proper rate limiting, input validation, and monitoring in place to detect and block abnormal request patterns.
🎯 Exploit Status
Exploitation requires valid user credentials. The vulnerability is publicly disclosed but no known public exploit code exists.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 10.11.9 or later
Vendor Advisory: https://mattermost.com/security-updates
Restart Required: Yes
Instructions:
1. Backup your Mattermost instance and database. 2. Download Mattermost version 10.11.9 or later from the official website. 3. Stop the Mattermost service. 4. Replace the existing installation with the patched version. 5. Restart the Mattermost service. 6. Verify the version is updated.
🔧 Temporary Workarounds
Rate Limiting Configuration
allImplement rate limiting on post creation endpoints to prevent rapid submission of large posts.
Configure in Mattermost config.json: "RateLimitSettings": {"Enable": true, "PerSec": 10, "MaxBurst": 100, "MemoryStoreSize": 10000, "VaryByRemoteAddr": true, "VaryByUser": true}
Input Validation via Reverse Proxy
linuxUse a reverse proxy like nginx or Apache to limit request body size and filter abnormal requests.
nginx: client_max_body_size 1M;
Apache: LimitRequestBody 1048576
🧯 If You Can't Patch
- Implement strict rate limiting on authenticated endpoints to prevent rapid submission of large posts.
- Monitor CPU usage and alert on abnormal spikes, particularly from single users making posts with unusually large content.
🔍 How to Verify
Check if Vulnerable:
Check Mattermost version via System Console > About or run: grep -i version /opt/mattermost/config/config.jsonCheck Version:
grep -i version /opt/mattermost/config/config.json | grep -o '[0-9]\+\.[0-9]\+\.[0-9]\+'Verify Fix Applied:
Verify version is 10.11.9 or higher and test by attempting to create a post with thousands of space-separated tokens (monitor CPU usage).📡 Detection & Monitoring
Log Indicators:
- Unusually large POST requests to message creation endpoints
- Multiple failed or slow requests from single user in short timeframe
- CPU usage spikes correlated with specific user activity
Network Indicators:
- HTTP POST requests with abnormally large body sizes (>1MB) to /api/v4/posts
- Rapid succession of POST requests from single IP/user
SIEM Query:
source="mattermost.log" AND "POST /api/v4/posts" AND content_length>1000000