CVE-2025-48940
📋 TL;DR
This vulnerability in MyBB forum software allows attackers to perform local file inclusion (LFI) through improper input validation in the upgrade component. Attackers can read arbitrary files from the server when the installer is unlocked and they have access to the upgrade script. All MyBB installations prior to version 1.8.39 are affected.
💻 Affected Systems
- MyBB
📦 What is this software?
Mybb by Mybb
⚠️ Risk & Real-World Impact
Worst Case
Complete server compromise through LFI leading to sensitive file disclosure, credential theft, and potential remote code execution via log poisoning or PHP wrappers.
Likely Case
Unauthorized reading of configuration files, database credentials, session data, and other sensitive server files.
If Mitigated
Limited impact if proper file permissions restrict sensitive file access and installer is locked.
🎯 Exploit Status
Exploitation requires specific conditions: unlocked installer and access to upgrade script. Admin authentication or fresh installation access needed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.8.39
Vendor Advisory: https://github.com/mybb/mybb/security/advisories/GHSA-q4jv-xwjx-37cp
Restart Required: No
Instructions:
1. Backup your MyBB installation and database. 2. Download MyBB 1.8.39 from mybb.com. 3. Replace all files except inc/config.php and inc/settings.php. 4. Run upgrade script if needed. 5. Verify installation works correctly.
🔧 Temporary Workarounds
Lock the installer
allCreate lock file to prevent installer access
touch install/lock
Remove installer directory
linuxDelete or restrict access to install directory after installation
rm -rf install/
🧯 If You Can't Patch
- Ensure install/lock file exists and is not writable by web server
- Restrict access to install directory via web server configuration or .htaccess
🔍 How to Verify
Check if Vulnerable:
Check MyBB version in Admin CP or inc/version.php. If version < 1.8.39 and install directory accessible, system is vulnerable.Check Version:
grep -E "'version'|'version_code'" inc/version.phpVerify Fix Applied:
Confirm version is 1.8.39+ and test that install directory returns 403/404 error when accessed.📡 Detection & Monitoring
Log Indicators:
- Unusual access to install/index.php with suspicious parameters
- Multiple failed upgrade attempts
- Access to sensitive files via web logs
Network Indicators:
- HTTP requests to install/index.php with file path parameters
- Unusual file read patterns from web server
SIEM Query:
web.url: "*install/index.php*" AND (web.querystring: "*file=*" OR web.querystring: "*path=*")