How to remediate – Windows HTTP Protocol Stack CVE-2022-21907 Mitigation (EnableT…

1. Introduction

The Windows HTTP Protocol Stack CVE-2022-21907 vulnerability allows a remote attacker to execute code on affected systems. This is because of a misconfiguration in the way HTTP requests are handled. Systems running web servers or any service using the Windows HTTP stack are at risk. Successful exploitation could lead to complete compromise of confidentiality, integrity and availability.

2. Technical Explanation

The vulnerability occurs when the ‘EnableTrailerSupport’ registry key is enabled. This allows specially crafted requests to be processed in a way that can overwrite memory and execute arbitrary code. An attacker needs to send malicious HTTP requests to a vulnerable system. The CVSS score for this vulnerability is currently unassigned, but it is considered important due to its potential impact.

• Root cause: The registry key HKLMSystemCurrentControlSetServicesHTTPParametersEnableTrailerSupport allows trailer headers which are not fully validated.
• Exploit mechanism: An attacker sends an HTTP request with a malicious trailer header, triggering a buffer overflow and code execution.
• Scope: Windows operating systems using the HTTP Protocol Stack are affected.

3. Detection and Assessment

You can check if your system is vulnerable by examining the registry settings. A thorough assessment involves scanning for the presence of the key.

• Quick checks: Use reg query to check the value of EnableTrailerSupport. Open an elevated command prompt and run: reg query "HKLMSystemCurrentControlSetServicesHTTPParameters" /v EnableTrailerSupport If the key exists, your system is potentially vulnerable.
• Scanning: Nessus plugin ID 16438 can detect this vulnerability. Other scanners may have similar checks.
• Logs and evidence: Check Windows event logs for unusual HTTP request activity or errors related to the HTTP stack.

reg query "HKLMSystemCurrentControlSetServicesHTTPParameters" /v EnableTrailerSupport

4. Solution / Remediation Steps

To fix this issue, you need to delete the ‘EnableTrailerSupport’ registry key if it exists.

4.1 Preparation

• The roll back plan is to re-create the registry value if needed, though this is not recommended.
• This change should be made during a scheduled maintenance window with appropriate approval from IT management.

4.2 Implementation

1. Step 1: Open an elevated command prompt.
2. Step 2: Delete the registry value using the following command: reg delete "HKLMSystemCurrentControlSetServicesHTTPParameters" /v EnableTrailerSupport /f

4.3 Config or Code Example

Before

reg query "HKLMSystemCurrentControlSetServicesHTTPParameters" /v EnableTrailerSupport

After

reg query "HKLMSystemCurrentControlSetServicesHTTPParameters" /v EnableTrailerSupport

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this type of issue.

• Practice 1: Least privilege reduces the impact if an attacker gains access.
• Practice 2: Regularly review and harden system configurations, including registry settings.

4.5 Automation (Optional)

A PowerShell script can be used to automate this fix.

# Check if the key exists
$keyPath = "HKLM:SystemCurrentControlSetServicesHTTPParameters"
if (Test-Path $keyPathEnableTrailerSupport) {
  # Delete the registry value
  Remove-ItemProperty -Path $keyPath -Name EnableTrailerSupport -Force
  Write-Host "Removed EnableTrailerSupport registry key."
} else {
  Write-Host "EnableTrailerSupport registry key does not exist."
}

5. Verification / Validation

Confirm the fix by checking that the registry value has been removed.

• Post-fix check: Run reg query "HKLMSystemCurrentControlSetServicesHTTPParameters" /v EnableTrailerSupport. The command should return an error indicating the key does not exist.
• Re-test: Re-run the initial registry query to confirm that the ‘EnableTrailerSupport’ key is no longer present.
• Monitoring: Monitor Windows event logs for any errors related to HTTP requests or stack operations.

reg query "HKLMSystemCurrentControlSetServicesHTTPParameters" /v EnableTrailerSupport

6. Preventive Measures and Monitoring

Update security baselines and implement regular configuration reviews.

• Baselines: Update your Windows security baseline to include this setting.
• Pipelines: Include checks in your CI/CD pipeline to ensure that the ‘EnableTrailerSupport’ key is not present on deployed systems.
• Asset and patch process: Review system configurations regularly as part of a vulnerability management program.

7. Risks, Side Effects, and Roll Back

Deleting this registry value may affect some older applications that rely on it. However, these are rare.

• Roll back: Re-create the ‘EnableTrailerSupport’ registry value with a DWORD value of 1 using the command: reg add "HKLMSystemCurrentControlSetServicesHTTPParameters" /v EnableTrailerSupport /t REG_DWORD /d 1 /f

8. References and Resources

Link only to sources that match this exact vulnerability.

• Vendor advisory or bulletin: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2022-21907
• NVD or CVE entry: https://nvd.nist.gov/vuln/detail/CVE-2022-21907
• Product or platform documentation relevant to the fix: https://learn.microsoft.com/en-us/troubleshoot/windows-server/http/event-id-4005