CVE-2023-53976
📋 TL;DR
This stored XSS vulnerability in myBB Forums allows authenticated administrators to inject malicious JavaScript into template titles. When these templates are viewed, the scripts execute in users' browsers, potentially compromising their sessions or accounts. Only administrators can exploit this, but all users viewing affected templates are at risk.
💻 Affected Systems
- myBB Forums
📦 What is this software?
Mybb by Mybb
⚠️ Risk & Real-World Impact
Worst Case
Administrator account compromise leading to full forum takeover, data theft, or malware distribution to all users.
Likely Case
Session hijacking of regular users, credential theft, or defacement of forum pages.
If Mitigated
Limited impact due to administrator-only exploitation and proper input validation.
🎯 Exploit Status
Exploit requires administrator credentials. Public exploit code exists in Exploit-DB.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.8.27 or later
Vendor Advisory: https://mybb.com/
Restart Required: No
Instructions:
1. Backup your forum database and files. 2. Download myBB 1.8.27+ from official site. 3. Replace all files except inc/config.php and uploads/. 4. Run upgrade script if needed.
🔧 Temporary Workarounds
Restrict Administrator Access
allLimit administrator accounts to trusted personnel only and implement strong authentication.
Input Validation Filter
allAdd custom input validation for template title fields to strip script tags.
🧯 If You Can't Patch
- Implement strict Content Security Policy (CSP) headers to block inline scripts.
- Monitor administrator activity logs for suspicious template modifications.
🔍 How to Verify
Check if Vulnerable:
Check if running myBB version 1.8.26 or earlier via Admin CP > Home > Version & Update.Check Version:
Check Admin CP or view inc/version.php file.Verify Fix Applied:
Verify version is 1.8.27+ and test template creation with script payloads.📡 Detection & Monitoring
Log Indicators:
- Unusual template creation/modification logs in Admin CP
- Suspicious strings in template titles containing script tags
Network Indicators:
- Unexpected JavaScript execution from template pages
- External script loads from template content
SIEM Query:
Search for 'template' AND 'title' AND ('script' OR 'javascript' OR 'onload=') in admin logs.