CVE-2024-39836
📋 TL;DR
This vulnerability allows remote/synthetic users created through shared channels to receive email notifications and reset passwords using munged email addresses. It affects Mattermost instances running vulnerable versions where shared channels are enabled, potentially enabling unauthorized account access.
💻 Affected Systems
- Mattermost
📦 What is this software?
Mattermost by Mattermost
Mattermost by Mattermost
Mattermost by Mattermost
Mattermost by Mattermost
⚠️ Risk & Real-World Impact
Worst Case
Attackers could reset passwords for synthetic users and gain unauthorized access to shared channel accounts, potentially accessing sensitive team communications and data.
Likely Case
Limited account compromise of synthetic users in shared channels, potentially disrupting collaboration or exposing channel-specific information.
If Mitigated
With proper email verification controls and monitoring, impact is limited to notification spam or failed password reset attempts.
🎯 Exploit Status
Exploitation requires access to shared channel functionality and knowledge of munged email addresses. No public exploits known at this time.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 9.9.2, 9.5.8, 9.10.1, 9.8.3 or later
Vendor Advisory: https://mattermost.com/security-updates
Restart Required: Yes
Instructions:
1. Backup Mattermost database and configuration. 2. Download patched version from Mattermost downloads page. 3. Stop Mattermost service. 4. Install updated version following Mattermost upgrade guide. 5. Restart Mattermost service. 6. Verify version and functionality.
🔧 Temporary Workarounds
Disable Shared Channels
allTemporarily disable shared channels feature to prevent creation of synthetic users
mmctl config set ExperimentalSettings.EnableSharedChannels false
Restrict Email Notifications
allConfigure email settings to restrict notifications for synthetic users
mmctl config set EmailSettings.EnableSignUpWithEmail false
mmctl config set EmailSettings.EnableSignInWithEmail false
🧯 If You Can't Patch
- Monitor authentication logs for unusual password reset attempts on synthetic user accounts
- Implement additional email verification steps for all password reset requests
🔍 How to Verify
Check if Vulnerable:
Check Mattermost version via System Console > About or run: mmctl versionCheck Version:
mmctl version | grep VersionVerify Fix Applied:
Verify version is 9.9.2+, 9.5.8+, 9.10.1+, or 9.8.3+. Test shared channel functionality with synthetic users.📡 Detection & Monitoring
Log Indicators:
- Unusual password reset attempts for synthetic users
- Email notifications sent to munged email addresses
- Failed authentication attempts followed by password resets
Network Indicators:
- Unusual SMTP traffic patterns for password reset emails
- Increased authentication requests to shared channel endpoints
SIEM Query:
source="mattermost" (event="password_reset" OR event="email_sent") user="*@sharedchannel*"