1. Introduction
Advantech WebAccess is a web application used for industrial automation and remote access. This vulnerability allows an unauthenticated attacker to bypass authentication, potentially gaining access to restricted pages, uploading malicious files, and deleting existing templates. Successful exploitation could compromise the confidentiality, integrity, and availability of systems running this software.
2. Technical Explanation
The Advantech WebAccess web server has an authentication bypass vulnerability in its WaExlViewer component due to improper handling of authentication requests. An attacker can send a specially crafted POST request that circumvents the intended access restrictions. This allows them to perform actions without valid credentials. The vulnerability is tracked as CVE-2017-5152.
- Root cause: Failure to properly manage authentication within the WaExlViewer component, specifically related to crafted POST requests.
- Exploit mechanism: An unauthenticated attacker sends a malicious POST request containing specific parameters that bypass the authentication check. This allows access to restricted functionality. For example, an attacker could send a POST request with manipulated parameters to upload a template file.
- Scope: Advantech WebAccess web servers running vulnerable versions of the WaExlViewer component.
3. Detection and Assessment
To confirm vulnerability, check the version of WebAccess installed. Thorough assessment involves attempting to exploit the bypass with a test request.
- Quick checks: Check the WebAccess application version through its user interface or by examining server configuration files.
- Scanning: Nessus plugin 95410 can detect this vulnerability. Tenable’s TRA-2017-04 provides detection guidance.
- Logs and evidence: Examine web server access logs for unusual POST requests targeting the WaExlViewer component, particularly those without valid authentication credentials.
# Example command placeholder:
# No direct command to check vulnerability; version check is UI based.
4. Solution / Remediation Steps
Apply a fix from the vendor to address this authentication bypass issue. Contact Advantech support for an updated version of WebAccess.
4.1 Preparation
- Stop the WebAccess service during the update process to ensure consistency. A roll back plan involves restoring from backup or reverting to the previous version.
- A change window may be required, depending on your environment and impact assessment. Approval should be obtained from relevant IT stakeholders.
4.2 Implementation
- Step 1: Download the latest patch or updated WebAccess package from Advantech’s support portal.
- Step 2: Stop the WebAccess service.
- Step 3: Install the downloaded patch or update the WebAccess installation.
- Step 4: Start the WebAccess service.
4.3 Config or Code Example
Before
# No specific config example available as this is a server-side vulnerability. The issue resides in the WaExlViewer component's code handling of authentication requests.
After
# After applying the patch, the WaExlViewer component will correctly handle authentication requests and prevent bypass attempts.
4.4 Security Practices Relevant to This Vulnerability
Implementing least privilege can reduce the impact of a successful exploit. Input validation is crucial for preventing malicious data from bypassing security checks. A regular patch cadence ensures timely application of security fixes.
- Practice 1: Least privilege – limit user access rights to only what is necessary, reducing potential damage if an attacker gains unauthorized access.
- Practice 2: Input validation – thoroughly validate all user inputs to prevent malicious data from being processed by the web application.
4.5 Automation (Optional)
# No automation script provided as this requires vendor-specific patching procedures.
5. Verification / Validation
- Post-fix check: Attempt a POST request with crafted parameters similar to those used in the original exploit attempt. The request should be blocked, and access denied.
- Re-test: Re-run the Nessus scan (plugin 95410) or use Tenable’s TRA-2017-04 guidance to confirm that the vulnerability is no longer detected.
- Smoke test: Verify that users can still log in and access authorized pages within WebAccess.
- Monitoring: Monitor web server logs for failed authentication attempts targeting the WaExlViewer component, which could indicate ongoing exploitation attempts.
# Post-fix command and expected output:
# Attempting a POST request with crafted parameters should result in an HTTP 403 Forbidden error or similar access denied response.
6. Preventive Measures and Monitoring
Update security baselines to include the latest patch for WebAccess. Implement regular vulnerability scanning as part of your CI/CD pipeline. Maintain a consistent patch review cycle based on risk assessment.
- Baselines: Update your security baseline or policy to require the latest WebAccess patch and configuration settings.
- Asset and patch process: Implement a regular patch review cycle of at least monthly for critical systems like industrial control applications.
7. Risks, Side Effects, and Roll Back
Applying the patch may cause temporary service downtime. Incompatibility with other software is possible but unlikely. To roll back, restore from backup or revert to the previous WebAccess version.
- Risk or side effect 1: Temporary service interruption during patching. Mitigation: Schedule patching during a maintenance window.
- Roll back: 1) Stop the WebAccess service. 2) Restore from backup or revert to the previous version of WebAccess. 3) Start the WebAccess service.
8. References and Resources
- Vendor advisory or bulletin: https://ics-cert.us-cert.gov/advisories/ICSA-17-012-01
- NVD or CVE entry: CVE-2017-5152
- Product or platform documentation relevant to the fix: No specific documentation available beyond vendor advisory.