1. Introduction
The Cisco Network Admission Control (NAC) Version vulnerability allows an attacker to obtain the version information of a remote Cisco device running NAC. This could allow attackers to identify devices with known vulnerabilities and target them specifically, potentially leading to further exploitation. Systems affected are typically Cisco Network Admission Control Managers. A successful exploit has a low impact on confidentiality, integrity, and availability as it only reveals version information.
2. Technical Explanation
The vulnerability occurs because the NAC Manager allows reading of its version via SSH connection. There is no authentication required to read this information. An attacker can connect to the switch using SSH and retrieve the version number. No CVE, CVSS or CWE are currently associated with this specific issue. A realistic example would be an attacker scanning a network for Cisco devices running NAC and then connecting to each device via SSH to determine its version.
- Root cause: Lack of authentication required to read the NAC version information.
- Exploit mechanism: An attacker connects to the switch using SSH and requests the version number.
- Scope: Cisco Network Admission Control (NAC) Managers are affected.
3. Detection and Assessment
To confirm if a system is vulnerable, you can check the NAC Manager’s version information via an SSH connection. A thorough method involves attempting to retrieve the version without authentication.
- Quick checks: Connect to the switch using SSH and attempt to read the version banner.
- Scanning: Nessus plugin ID 138670 can be used as an example for identifying Cisco NAC devices.
- Logs and evidence: Review SSH logs for connections attempting to retrieve version information, although this may not always be logged.
ssh show version 4. Solution / Remediation Steps
The following steps provide a precise method to address the issue.
4.1 Preparation
- Change window needs and approval may be required depending on your organization’s policies.
4.2 Implementation
4.3 Config or Code Example
Before
After
line vty 0 4
authentication required
login local
!
line console 0
authentication required
login local
4.4 Security Practices Relevant to This Vulnerability
Several security practices can help prevent this type of vulnerability.
- Practice 1: Least privilege – Limit SSH access to only authorized personnel and services.
- Practice 2: Secure defaults – Configure secure default settings for all network devices, including requiring authentication for management interfaces.
4.5 Automation (Optional)
Automation is not directly applicable to this vulnerability due to the configuration change required. However, tools like Ansible can be used to push SSH configurations across multiple Cisco devices.
5. Verification / Validation
- Post-fix check: Connect to the switch using SSH and attempt to read the version banner. Authentication should now be required.
- Monitoring: Monitor SSH logs for failed login attempts, which could indicate unauthorized access attempts.
ssh show version 6. Preventive Measures and Monitoring
Update security baselines to include requiring authentication for all network device management interfaces.
- Baselines: Update your security baseline or policy to require authentication for SSH access on Cisco devices.
- Pipelines: Include checks in CI/CD pipelines to ensure that secure default configurations are applied during deployment.
- Asset and patch process: Implement a regular review cycle for network device configurations to identify and address potential vulnerabilities.
7. Risks, Side Effects, and Roll Back
Implementing SSH authentication may disrupt existing automation scripts or monitoring tools that rely on unauthenticated access.
- Risk or side effect 1: Disruption of existing automation scripts – Ensure all scripts are updated to use proper authentication credentials.
- Roll back: Remove the “authentication required” command from the SSH configuration to restore unauthenticated access.
8. References and Resources
Links related to this vulnerability.
- Vendor advisory or bulletin: Cisco Security Advisories
- NVD or CVE entry: No specific CVE currently exists for this issue.
- Product or platform documentation relevant to the fix: Cisco IOS Security Command Reference