1. Introduction
The Advantech WebAccess/SCADA Network Service vulnerability (webvrpcs.exe Arbitrary File Download) allows a remote, unauthenticated attacker to download arbitrary files from a vulnerable system. This could lead to sensitive information disclosure and potential compromise of the SCADA environment. Systems running affected versions of Advantech WebAccess are at risk. Impact is high on confidentiality, integrity and availability.
2. Technical Explanation
The vulnerability stems from improper validation of user-supplied data within the DCERPC request processing in webvrpcs.exe. An attacker can craft a series of malicious requests to bypass security checks and force the service to download files from arbitrary locations accessible by the system account running the WebAccess service. CVE-2019-3941 describes this issue.
- Root cause: Insufficient input validation when handling DCERPC requests allows for manipulation of file paths.
- Exploit mechanism: An attacker sends crafted DCERPC requests to webvrpcs.exe, specifying a malicious file path that points to sensitive data on the system.
- Scope: Advantech WebAccess SCADA Network Service (webvrpcs.exe) is affected. Specific versions are not detailed in the provided context.
3. Detection and Assessment
Confirming vulnerability requires checking the running version of webvrpcs.exe and assessing network accessibility. A thorough assessment involves monitoring for suspicious DCERPC traffic.
- Quick checks: Use Task Manager to identify if webvrpcs.exe is running.
- Scanning: Tenable Nessus plugin ID 128695 can detect this vulnerability, but results should be verified.
- Logs and evidence: Check Windows Event Logs for unusual activity related to webvrpcs.exe or DCERPC traffic.
tasklist | findstr webvrpcs.exe4. Solution / Remediation Steps
The primary solution is to contact Advantech for a patch or updated configuration. The following steps outline preparation and verification.
4.1 Preparation
- Ensure you have a rollback plan in place to restore from backup if needed. Coordinate with relevant stakeholders for change approval.
4.2 Implementation
- Step 1: Contact Advantech support and request the latest security patch or configuration update for WebAccess.
- Step 2: Once received, apply the patch or implement the updated configuration according to Advantech’s instructions.
4.3 Config or Code Example
No config or code example is available as the solution requires a patch from Advantech.
4.4 Security Practices Relevant to This Vulnerability
Several security practices can help mitigate this type of vulnerability. Least privilege limits damage if exploited, and input validation prevents unsafe data reaching the service.
- Practice 1: Implement least privilege for the WebAccess service account, restricting its access only to necessary files and resources.
- Practice 2: Regularly review and validate all user inputs to prevent malicious data from being processed by the service.
4.5 Automation (Optional)
No automation script is available as this requires a vendor patch.
5. Verification / Validation
Verify the fix by confirming the updated version of webvrpcs.exe and re-running detection methods. A smoke test confirms core functionality remains operational.
- Post-fix check: Use Task Manager to confirm that webvrpcs.exe is running with the latest patch applied (version details from Advantech).
- Re-test: Re-run the Tenable Nessus scan (plugin ID 128695) and verify it no longer reports the vulnerability.
tasklist | findstr webvrpcs.exe6. Preventive Measures and Monitoring
Regular security baselines, patching processes, and monitoring for suspicious activity can help prevent future exploitation of similar vulnerabilities.
- Baselines: Update your system baseline to include the latest security patches and configurations from Advantech.
- Asset and patch process: Establish a regular patch review cycle for all SCADA systems, prioritizing critical vulnerabilities like this one.
7. Risks, Side Effects, and Roll Back
Applying patches can sometimes cause service disruptions or compatibility issues. Always have a rollback plan in place.
- Risk or side effect 1: Patching may temporarily interrupt WebAccess service availability. Schedule patching during a maintenance window.
- Risk or side effect 2: Incompatibility with other software components is possible, though unlikely. Test the patch in a non-production environment first.
- Roll back: Restore from backup if the patch causes issues. Revert to the previous version of webvrpcs.exe and configuration files.
8. References and Resources
Refer to official advisories for accurate information about this vulnerability.
- Vendor advisory or bulletin: https://www.tenable.com/security/research/tra-2019-15
- NVD or CVE entry: CVE-2019-3941