1. Introduction
The WMI IIS ISAPI Extension Enumeration vulnerability means that information about Internet Information Services (IIS) extensions installed on a server can be discovered remotely. This matters because attackers could use this information to identify potential weaknesses and exploit them. Systems running IIS, particularly web servers, are usually affected. A successful attack could allow an attacker to gain information about the system configuration, potentially leading to further compromise of confidentiality, integrity, and availability.
2. Technical Explanation
The vulnerability occurs because IIS allows enumeration of ISAPI extensions through Windows Management Instrumentation (WMI). Attackers can query WMI to list these extensions and determine whether they are enabled or disabled. There is no known CVE associated with this specific enumeration, but it’s a reconnaissance step often preceding exploitation of vulnerable ISAPI extensions. An attacker could use PowerShell to remotely query the IIS configuration for installed extensions. Affected systems include those running any version of IIS with ISAPI filters enabled.
- Root cause: The WMI interface exposes information about IIS configurations without sufficient restriction.
- Exploit mechanism: An attacker uses a remote WMI query to list the installed ISAPI extensions and their status (enabled/disabled). This is often followed by attempts to exploit known vulnerabilities in those extensions. For example, an attacker could use PowerShell like this:
Get-WmiObject win32_iiswebappsetting | select name, siteid - Scope: All versions of IIS with ISAPI filters enabled are potentially affected.
3. Detection and Assessment
You can confirm a system is vulnerable by checking for the presence of ISAPI extensions in the IIS configuration. A quick check involves listing installed web applications, which will reveal if ISAPI extensions are being used. A thorough method involves examining the `applicationHost.config` file directly.
- Quick checks: Use PowerShell to list web applications:
Get-WmiObject win32_iiswebappsetting | select name, siteidThis will show if any web applications are installed, indicating ISAPI extensions may be present. - Scanning: Nessus plugin ID 10425 can detect this issue as an information disclosure vulnerability. Other scanners may have similar checks.
- Logs and evidence: Examine the IIS logs for WMI queries related to `win32_iiswebappsetting`. Look for requests originating from unexpected sources. Event IDs are not typically associated with this specific enumeration.
Get-WmiObject win32_iiswebappsetting | select name, siteid4. Solution / Remediation Steps
The best way to address this vulnerability is to limit access to WMI and review the need for ISAPI extensions. Removing unnecessary extensions reduces the attack surface.
4.1 Preparation
- Ensure you have access to the server’s configuration files and appropriate permissions. A roll back plan involves restoring the backed-up `applicationHost.config` file and restarting the IIS service.
- Changes should be made during a scheduled maintenance window with approval from relevant IT stakeholders.
4.2 Implementation
- Step 1: Review installed ISAPI extensions using PowerShell:
Get-WmiObject win32_iiswebappsetting | select name, siteid. Identify any unnecessary or outdated extensions. - Step 2: Remove unused ISAPI extensions from the IIS configuration through the IIS Manager GUI or by editing the `applicationHost.config` file.
- Step 3: Restrict access to WMI using Windows Firewall or Group Policy, limiting access to only authorized users and services.
4.3 Config or Code Example
Before
<system.webServer> <isapiFilters> <add filterName="ASPNet_Filter" ... /> </isapiFilters> </system.webServer>After
<system.webServer> <isapiFilters> </isapiFilters> </system.webServer>4.4 Security Practices Relevant to This Vulnerability
- Practice 1: Least privilege – restrict access to WMI and IIS configuration files to only authorized personnel.
- Practice 2: Patch cadence – regularly update IIS with the latest security patches to address known vulnerabilities in ISAPI extensions.
4.5 Automation (Optional)
# PowerShell example to remove an ISAPI extension (replace with your specific filter name)
# Caution: This will permanently delete the extension configuration. Test thoroughly before deploying in production.
# Get-WmiObject win32_iiswebappsetting | Where-Object {$_.name -eq "UnwantedExtension"} | Remove-Item5. Verification / Validation
Confirm the fix by re-running the initial detection method and verifying that the ISAPI extensions are no longer enumerable via WMI. Perform a simple service smoke test to ensure web applications continue to function correctly.
- Post-fix check: Run
Get-WmiObject win32_iiswebappsetting | select name, siteidand confirm that the unwanted extensions are no longer listed. - Re-test: Re-run the initial WMI query to ensure the enumeration is blocked or returns an empty result.
- Smoke test: Access key web applications through a browser to verify functionality. Check for error pages or broken features.
- Monitoring: Monitor IIS logs for unexpected WMI queries related to `win32_iiswebappsetting`. An alert could be triggered if such queries are detected from unauthorized sources.
Get-WmiObject win32_iiswebappsetting | select name, siteid6. Preventive Measures and Monitoring
- Baselines: Update your server security baseline to include restrictions on WMI access and a list of approved ISAPI extensions.
- Asset and patch process: Implement a regular patch review cycle for IIS and its components, ensuring timely application of security updates.
7. Risks, Side Effects, and Roll Back
- Roll back: Restore the backed-up `applicationHost.config` file and restart the IIS service to revert any configuration changes. If WMI access was restricted, re-enable it for authorized users and services.
8. References and Resources
- Vendor advisory or bulletin: http://www.iis.net/configreference/system.webserver/isapifilters
- NVD or CVE entry: No specific CVE is associated with this enumeration vulnerability.
- Product or platform documentation relevant to the fix: https://learn.microsoft.com/en-us/iis/config