CVE-2023-25135
📋 TL;DR
CVE-2023-25135 is a critical remote code execution vulnerability in vBulletin that allows unauthenticated attackers to execute arbitrary code via crafted HTTP requests. This occurs due to insecure deserialization in the verify_serialized function. All vBulletin installations before the patched versions are affected.
💻 Affected Systems
- vBulletin
📦 What is this software?
Vbulletin by Vbulletin
Vbulletin by Vbulletin
Vbulletin by Vbulletin
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise allowing attackers to install malware, steal data, pivot to other systems, and maintain persistent access.
Likely Case
Web server compromise leading to data theft, defacement, or use as part of a botnet.
If Mitigated
Attack blocked at network perimeter or detected before exploitation.
🎯 Exploit Status
Public exploit code exists and requires minimal technical skill to execute.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 5.6.7 PL1, 5.6.8 PL1, or 5.6.9 PL1
Vendor Advisory: https://forum.vbulletin.com/forum/vbulletin-announcements/vbulletin-announcements_aa/4473890-vbulletin-5-6-9-security-patch
Restart Required: No
Instructions:
1. Download the appropriate patched version from vBulletin customer area. 2. Backup your current installation. 3. Upload and overwrite files with patched version. 4. Clear system cache in AdminCP.
🔧 Temporary Workarounds
WAF Rule Implementation
allBlock serialized data in HTTP requests using web application firewall rules.
WAF-specific rules to block unserialize() patterns in request payloads
Input Validation Filter
allAdd custom PHP filter to block serialized data in requests.
Add input validation in vBulletin code to reject serialized strings
🧯 If You Can't Patch
- Implement strict WAF rules to block serialized data patterns in HTTP requests
- Restrict access to vBulletin installation using IP whitelisting or authentication gateways
🔍 How to Verify
Check if Vulnerable:
Check vBulletin version in AdminCP or via version.php file. If version is below 5.6.7 PL1, 5.6.8 PL1, or 5.6.9 PL1, system is vulnerable.Check Version:
Check /core/includes/version.php or AdminCP → Maintenance → View PHP InfoVerify Fix Applied:
Confirm version shows 5.6.7 PL1, 5.6.8 PL1, or 5.6.9 PL1 in AdminCP. Test with known safe payloads if available.📡 Detection & Monitoring
Log Indicators:
- HTTP requests containing serialized PHP objects
- Unusual POST requests to vBulletin endpoints
- Error logs showing unserialize() failures
Network Indicators:
- HTTP requests with serialized data patterns (O: followed by numbers)
- Unusual traffic spikes to vBulletin installation
SIEM Query:
source="web_logs" AND (uri="*ajax/api*" OR uri="*ajax/render*") AND (request_body="*O:*" OR request_body="*a:*" OR request_body="*s:*")🔗 References
- https://forum.vbulletin.com/forum/vbulletin-announcements/vbulletin-announcements_aa/4473890-vbulletin-5-6-9-security-patch
- https://www.ambionics.io/blog/vbulletin-unserializable-but-unreachable
- https://forum.vbulletin.com/forum/vbulletin-announcements/vbulletin-announcements_aa/4473890-vbulletin-5-6-9-security-patch
- https://www.ambionics.io/blog/vbulletin-unserializable-but-unreachable
