CVE-2023-53977
📋 TL;DR
This stored XSS vulnerability in myBB Forums allows authenticated administrators to inject malicious JavaScript when creating new forums. The injected scripts execute when other users view the forum listing, potentially compromising their accounts or sessions. Only myBB installations with version 1.8.26 are affected.
💻 Affected Systems
- myBB Forums
📦 What is this software?
Mybb by Mybb
⚠️ Risk & Real-World Impact
Worst Case
Attackers could steal administrator credentials, hijack user sessions, deface forums, or redirect users to malicious sites, potentially leading to complete forum compromise.
Likely Case
Attackers with admin access could inject scripts to steal user session cookies or credentials, leading to account takeover of regular users viewing the forum listing.
If Mitigated
With proper input validation and output encoding, the malicious scripts would be rendered harmless as text rather than executable code.
🎯 Exploit Status
Exploitation requires administrator credentials. The vulnerability is simple to exploit once admin access is obtained.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.8.27 or later
Vendor Advisory: https://mybb.com/
Restart Required: No
Instructions:
1. Backup your myBB installation and database. 2. Download myBB 1.8.27 or later from the official website. 3. Replace all files with the new version (except config files). 4. Run the upgrade script if required. 5. Clear template cache in Admin CP.
🔧 Temporary Workarounds
Input Validation Filter
allAdd custom input validation to sanitize forum title fields before processing
Modify inc/plugins/forum.php to add htmlspecialchars() or similar filtering to forum title inputs
🧯 If You Can't Patch
- Restrict administrator accounts to trusted personnel only and implement strong authentication
- Monitor forum creation logs for suspicious activity and unusual forum titles
🔍 How to Verify
Check if Vulnerable:
Check Admin CP > Version & Update for version number. If version is exactly 1.8.26, you are vulnerable.Check Version:
Check Admin CP dashboard or view inc/version.php fileVerify Fix Applied:
After updating, verify version shows 1.8.27 or later in Admin CP. Test forum creation with script tags to ensure they are properly sanitized.📡 Detection & Monitoring
Log Indicators:
- Unusual forum creation events
- Forum titles containing script tags or JavaScript code
- Multiple forum creations in short time
Network Indicators:
- Unexpected JavaScript execution in forum pages
- External script loading from forum listings
SIEM Query:
source="mybb_logs" AND (event="forum_created" AND title CONTAINS "<script" OR title CONTAINS "javascript:")