How to remediate – SNMP Request Cisco Router Information Disclosure

1. Introduction

The SNMP Request Cisco Router Information Disclosure vulnerability allows an attacker to determine the model of a remote CISCO router. This information can be used to gather more details about the system, potentially aiding in further attacks. Systems affected are typically Cisco routers running SNMP. A successful exploit could lead to increased reconnaissance and potential compromise of network devices. Confidentiality may be impacted through disclosure of device information.

2. Technical Explanation

This vulnerability occurs because the model number of a Cisco router is accessible via Simple Network Management Protocol (SNMP) requests using OID 1.3.6.1.4.1.9.1. An attacker can query this OID to retrieve the device’s model information without authentication if SNMP is not properly secured. There is no known CVE associated with this specific disclosure, but it represents a common misconfiguration risk.

• Root cause: Unrestricted access to system information via SNMP.
• Exploit mechanism: An attacker sends an SNMP query using the OID 1.3.6.1.4.1.9.1 to the target Cisco router. The response contains the device model number. For example, a simple `snmpget` command can retrieve this information.
• Scope: Cisco routers with SNMP enabled are affected.

3. Detection and Assessment

You can confirm if your system is vulnerable by checking whether SNMP is enabled and accessible. A thorough method involves attempting to query the OID directly.

• Quick checks: Use `show running-config | include snmp` on a Cisco router to check if SNMP is configured.
• Scanning: Nessus plugin ID 10879 can detect this vulnerability as an example.
• Logs and evidence: Check firewall logs for UDP traffic on port 161 originating from unknown sources attempting to query the router.

snmpget -v2c -c public  1.3.6.1.4.1.9.1

4. Solution / Remediation Steps

The best way to fix this issue is to disable SNMP if it’s not needed, or restrict access using Access Control Lists (ACLs).

4.1 Preparation

• Dependencies: Ensure you have console or SSH access to the router. A roll back plan is to restore the previous configuration.
• Change window needs: Consider a maintenance window as service interruption may occur during configuration changes. Approval from the network team may be required.

4.2 Implementation

1. Step 1: Disable SNMP if not in use by entering `no snmp-server community public RW` and `no ip snmp trap receiver`.
2. Step 2: If SNMP is required, configure access control lists (ACLs) to restrict access to trusted IP addresses. For example, create an ACL permitting only specific management stations.

4.3 Config or Code Example

Before

snmp-server community public RW
ip snmp trap receiver 0.0.0.0/24 version 1 public

After

no snmp-server community public RW
access-list 10 permit ip  0.0.0.0 wildcard 0.0.0.0
snmp-server access-group 10

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this issue.

• Practice 1: Least privilege – only enable services that are absolutely necessary and restrict access to those services.
• Practice 2: Safe defaults – change default community strings and SNMP settings.

4.5 Automation (Optional)

# Example Ansible snippet - use with caution!
- name: Disable SNMP on Cisco routers
  cisco.ios.ios_config:
    lines:
      - no snmp-server community public RW
      - no ip snmp trap receiver
  become: yes

5. Verification / Validation

Confirm the fix by checking that SNMP is disabled or access is restricted.

• Post-fix check: Run `show running-config | include snmp` and verify that SNMP community strings are removed or ACLs are in place.
• Re-test: Attempt to query the OID 1.3.6.1.4.1.9.1 again using `snmpget`. The query should now fail due to disabled service or access restrictions.
• Smoke test: Ensure any legitimate SNMP monitoring tools still function correctly if SNMP is not completely disabled.
• Monitoring: Monitor firewall logs for blocked SNMP traffic from untrusted sources as an example.

snmpget -v2c -c public  1.3.6.1.4.1.9.1 # Should now timeout or return "No Such Name"

6. Preventive Measures and Monitoring

Update security baselines to include SNMP hardening guidelines for example.

• Baselines: Update your router configuration baseline to enforce disabling unnecessary services like SNMP, or restricting access using ACLs.
• Pipelines: Implement CI/CD pipeline checks to scan router configurations for insecure SNMP settings.
• Asset and patch process: Review router configurations regularly as part of a vulnerability management program.

7. Risks, Side Effects, and Roll Back

Disabling SNMP may impact network monitoring tools that rely on it.

• Risk or side effect 1: Disabling SNMP could break existing monitoring systems. Mitigation is to configure SNMP with appropriate access controls instead of disabling it entirely.
• Roll back: Restore the previous router configuration from backup if issues occur.

8. References and Resources

Link only to sources that match this exact vulnerability.

• Vendor advisory or bulletin: ftp://ftp.cisco.com/pub/mibs/v1/CISCO-PRODUCTS-MIB-V1SMI.my
• NVD or CVE entry: Not applicable for this specific disclosure.
• Product or platform documentation relevant to the fix: ftp://ftp.cisco.com/pub/mibs/v2/CISCO-PRODUCTS-MIB.my