1. Introduction
vBulletin CVE-2019-16759 Bypass Remote Code Execution (CVE-2019-16759) is a flaw in the vBulletin bulletin board system that allows an attacker to execute code on the server remotely. This affects businesses running vulnerable vBulletin installations, potentially leading to complete system compromise. Systems usually affected are web servers hosting vBulletin forums. A successful exploit could result in loss of confidentiality, integrity and availability of data.
2. Technical Explanation
The vulnerability is an input-validation flaw within the ajax/render/widget_php API. This allows for remote code execution because unsanitised data can be passed to PHP functions. An attacker could send a crafted request to execute arbitrary code on the server. CVE-2019-16759 and CVE-2020-17496 both describe this issue.
- Root cause: Missing input validation in the ajax/render/widget_php API allows for execution of PHP code.
- Exploit mechanism: An attacker sends a malicious HTTP request to the vulnerable endpoint, containing crafted data that is then executed as PHP code. For example, an attacker could inject PHP code into a widget parameter.
- Scope: vBulletin versions prior to 6.0.7 are affected.
3. Detection and Assessment
You can confirm if your system is vulnerable by checking the installed vBulletin version. A thorough method involves using a vulnerability scanner.
- Quick checks: Check the vBulletin version in the admin control panel under ‘Server Information’.
- Scanning: Nessus plugin ID 62dedb88 can detect this vulnerability. This is an example only.
- Logs and evidence: Look for suspicious activity related to the ajax/render/widget_php API in your web server logs.
# Example command placeholder:
# No specific command available, check vBulletin admin panel version.
4. Solution / Remediation Steps
To fix this issue, disable PHP widgets or contact the vendor for an update.
4.1 Preparation
- Ensure you have access to the vBulletin admin control panel or server configuration files. A roll back plan is to restore from the earlier backup.
- A change window may be needed, depending on your organisation’s policies. Approval from a senior IT administrator might be required.
4.2 Implementation
- Step 1: Log in to the vBulletin admin control panel.
- Step 2: Navigate to ‘Settings’ then ‘Options’.
- Step 3: Search for ‘PHP Widgets’ and disable them.
- Step 4: Save your changes. Alternatively, contact the vendor for an update if available.
4.3 Config or Code Example
Before
// PHP Widgets enabled (example configuration)
$config['widget_php_enabled'] = 1;
After
// PHP Widgets disabled (example configuration)
$config['widget_php_enabled'] = 0;
4.4 Security Practices Relevant to This Vulnerability
Several security practices can help prevent this type of issue. Least privilege reduces the impact if exploited, and input validation blocks unsafe data.
- Practice 1: Implement least privilege principles for all server accounts.
- Practice 2: Enforce strict input validation on all user-supplied data.
4.5 Automation (Optional)
No suitable automation script is available at this time.
5. Verification / Validation
Confirm the fix by checking that PHP widgets are disabled and re-running the vulnerability scan. A simple service smoke test involves accessing your forum to ensure basic functionality remains.
- Post-fix check: Verify in the vBulletin admin control panel under ‘Settings’ then ‘Options’ that ‘PHP Widgets’ is set to disabled.
- Re-test: Re-run the Nessus scan (plugin ID 62dedb88) and confirm it no longer reports the vulnerability.
- Smoke test: Access your forum homepage and verify you can view posts and navigate categories.
- Monitoring: Monitor web server logs for any suspicious activity related to PHP execution in the ajax/render directory. This is an example only.
# Post-fix command and expected output
# No specific command available, check vBulletin admin panel version.
6. Preventive Measures and Monitoring
Update your security baseline to include a requirement for disabling PHP widgets in vBulletin. Add checks in your CI/CD pipeline to prevent vulnerable versions of vBulletin from being deployed.
- Baselines: Update your security baseline or policy to require disabling PHP Widgets in vBulletin installations.
- Pipelines: Implement SAST and SCA tools in your CI/CD pipeline to identify vulnerable components like outdated vBulletin versions.
- Asset and patch process: Review and apply patches for vBulletin on a regular basis, at least monthly.
7. Risks, Side Effects, and Roll Back
Disabling PHP widgets may break some forum functionality if you are using them. The roll back steps involve re-enabling the widgets in the admin control panel.
- Risk or side effect 1: Disabling PHP widgets could affect forum features that rely on them.
- Risk or side effect 2: Users may experience reduced functionality if they relied on PHP widgets.
- Roll back: Step 1: Log in to the vBulletin admin control panel. Step 2: Navigate to ‘Settings’ then ‘Options’. Step 3: Search for ‘PHP Widgets’ and re-enable them. Step 4: Save your changes.
8. References and Resources
Links only to sources that match this exact vulnerability.
- Vendor advisory or bulletin: https://www.vbulletin.com/forum/showthread.php?t=359621
- NVD or CVE entry: https://nvd.nist.gov/vuln/detail/CVE-2019-16759
- Product or platform documentation relevant to the fix: https://www.vbulletin.com/forum/showthread.php?t=359621