How to remediate – MDG Web Server 4D GET Request Remote Overflow

1. Introduction

The MDG Web Server 4D GET Request Remote Overflow vulnerability allows a remote attacker to crash the web server by sending an excessively long string via a GET request. This can lead to a denial of service, disrupting services for legitimate users. Systems running MDG Web Server 4D are affected. A successful attack could cause availability issues.

2. Technical Explanation

The vulnerability occurs because the web server does not properly validate the length of input received in GET requests. An attacker can send a string containing many ‘<' characters, exceeding the server’s buffer capacity and causing it to crash. This is a remote exploit requiring no authentication.

• Root cause: Insufficient input validation on GET request parameters.
• Exploit mechanism: Sending an oversized string of ‘<' characters in a GET request causes a buffer overflow, leading to server termination. For example, a request like http://example.com/?param= could trigger the vulnerability.
• Scope: MDG Web Server 4D is affected. Specific versions are not currently known.

3. Detection and Assessment

Confirming vulnerability requires checking the running version of MDG Web Server 4D and testing its response to oversized GET requests.

• Quick checks: Check the web server’s ‘About’ page or configuration files for the installed version number.
• Scanning: Nessus plugin ID 30895 may detect this vulnerability as an example only.
• Logs and evidence: Look for crashes or errors in the web server logs, specifically related to GET request processing. Event IDs are not currently known.

# No specific command available without knowing the OS/server setup. Check version via UI or config files.

4. Solution / Remediation Steps

Currently, there is no known solution for this vulnerability. Mitigation focuses on limiting exposure and monitoring for attacks.

4.1 Preparation

• Dependencies: No specific dependencies exist. Roll back plan: Restore from backup or revert configuration changes.
• Change window needs and approval may be required depending on your organisation’s policies.

4.2 Implementation

1. Step 1: Monitor web server logs for suspicious activity, particularly GET requests with very long parameters.
2. Step 2: Implement a Web Application Firewall (WAF) rule to block requests exceeding a reasonable length limit.

4.3 Config or Code Example

Before

# No configuration example available as there is no known fix.

After

# WAF rule example (syntax varies by vendor): Block requests with parameter length > 256 characters.

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help mitigate the risk of this vulnerability type.

• Practice 1: Input validation is crucial for preventing buffer overflows and other injection attacks.
• Practice 2: Least privilege reduces the impact if an attacker successfully exploits a vulnerability.

4.5 Automation (Optional)

No suitable automation script exists at this time due to the lack of a defined fix.

# No script available as there is no known solution.

5. Verification / Validation

Verification involves confirming that the WAF rule blocks oversized requests and monitoring logs for blocked attempts.

• Post-fix check: Verify the WAF is active and configured correctly.
• Re-test: Attempt to send an oversized GET request (e.g., http://example.com/?param=) and confirm it is blocked by the WAF.
• Monitoring: Monitor WAF logs for blocked requests matching the pattern of oversized GET parameters as an example only.

# WAF log output should show a blocked request with the long parameter.

6. Preventive Measures and Monitoring

Regular security assessments and patch management are essential to prevent similar vulnerabilities.

• Baselines: Update your web server baseline configuration to include input validation rules.
• Pipelines: Implement Static Application Security Testing (SAST) tools in your CI/CD pipeline to identify potential vulnerabilities early.
• Asset and patch process: Establish a regular patch review cycle for all web servers.

7. Risks, Side Effects, and Roll Back

Implementing WAF rules may cause false positives, blocking legitimate traffic.

• Risk or side effect 2: Incorrectly configured WAF rules can impact web server performance.
• Roll back: Remove or adjust the WAF rule if false positives occur. Restore the previous configuration if necessary.

8. References and Resources

Links to resources related to this specific vulnerability.

• Vendor advisory or bulletin: No official advisory is currently available.
• NVD or CVE entry: No CVE has been assigned as of 2024-01-26.
• Product or platform documentation relevant to the fix: https://seclists.org/fulldisclosure/2003/May/3