1. Introduction
The Zyxel Router Command Injection Vulnerability (CVE-2017-6884) affects certain Zyxel routers, allowing a remote attacker to execute commands on the device. This is due to insufficient input validation in the diagnostic tools. Successful exploitation could lead to complete system compromise, impacting confidentiality, integrity and availability of network services.
2. Technical Explanation
- Root cause: Missing input validation within the nslookup function allows arbitrary command execution.
- Exploit mechanism: An attacker sends a specially crafted HTTP request containing malicious commands embedded within parameters passed to the diagnostic tools. For example, an attacker could inject a command like “; ls -la /” into an HTTP GET request.
- Scope: Affected Zyxel routers include those running vulnerable firmware revisions. Specific models are not detailed in this information.
3. Detection and Assessment
Confirming vulnerability requires checking the router’s firmware version. A thorough assessment involves reviewing logs for suspicious activity.
- Quick checks: Access the router’s web interface and navigate to System Information or Firmware Version to identify the current build.
- Scanning: Nessus plugin ID 2b6a48e7 can detect this vulnerability, but results should be verified manually.
- Logs and evidence: Examine router logs for unusual processes or commands executed by authenticated users. Specific log paths are not detailed in this information.
4. Solution / Remediation Steps
The primary solution is to contact Zyxel for updated firmware and remediation instructions.
4.1 Preparation
- Ensure you have valid router credentials and network access. A roll back plan involves restoring from the previous configuration backup if issues occur.
- Change windows may be required depending on business impact, with approval needed from IT management.
4.2 Implementation
- Step 2: Access the router’s web interface and navigate to the Firmware Upgrade section.
- Step 3: Upload the downloaded firmware file and initiate the upgrade process.
4.3 Config or Code Example
Before
After
4.4 Security Practices Relevant to This Vulnerability
Practices such as least privilege and input validation are relevant to mitigating this type of vulnerability.
- Practice 1: Implement the principle of least privilege, limiting user access rights to only those necessary for their tasks.
- Practice 2: Enforce strict input validation on all user-supplied data to prevent malicious commands from being injected.
4.5 Automation (Optional)
Automation is not applicable in this case, as the fix requires manual firmware updates provided by the vendor.
5. Verification / Validation
Confirm the fix by verifying the updated firmware version and re-testing for vulnerability.
- Post-fix check: Access the router’s web interface and confirm that the firmware version has been updated to a patched release.
- Re-test: Run Nessus plugin ID 2b6a48e7 again; it should no longer report the vulnerability.
- Smoke test: Verify basic network connectivity, such as internet access and internal resource access.
- Monitoring: Monitor router logs for any unusual activity or failed login attempts.
6. Preventive Measures and Monitoring
Regular security baselines and patch management are important preventative measures.
- Baselines: Update your security baseline to include the latest firmware versions for all Zyxel routers.
- Asset and patch process: Implement a regular patch management cycle to ensure timely updates of all network devices.
7. Risks, Side Effects, and Roll Back
Firmware upgrades can sometimes cause service disruptions or require reconfiguration.
- Risk or side effect 1: Firmware upgrade may temporarily interrupt network connectivity. Mitigate by performing the upgrade during a maintenance window.
- Risk or side effect 2: Incorrect firmware installation could brick the device. Mitigate by following Zyxel’s official instructions carefully.
8. References and Resources
Links to relevant resources for this vulnerability.
- Vendor advisory or bulletin: Not specified in provided context.
- NVD or CVE entry: CVE-2017-6884
- Product or platform documentation relevant to the fix: Not specified in provided context.