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How to remediate – SNMP Query WLAN SSID (Cisco)

Contents

1. Introduction

The SNMP Query WLAN SSID (Cisco) vulnerability allows an attacker to obtain the Service Set Identifier (SSID) of a wireless LAN through Simple Network Management Protocol (SNMP) requests. This information can aid in reconnaissance and potentially lead to further attacks on the network. Cisco Access Points are typically affected. A successful exploit could compromise the confidentiality of the wireless network by revealing its name.

2. Technical Explanation

The vulnerability occurs because the SSID is exposed via SNMP, specifically through Object Identifier (OID) 1.3.6.1.4.1.9.9.512.1.1.1.1.4.1 on Cisco Access Point controllers. An attacker can query this OID to retrieve the WLAN’s SSID without authentication if SNMP is enabled with default community strings or weak access controls. There is no known Common Vulnerabilities and Exposures (CVE) associated with this specific issue, but it relates to insecure configurations of SNMP.

  • Root cause: The system information about the remote WLAN is accessible via SNMP requests without sufficient security measures.
  • Exploit mechanism: An attacker sends an SNMP query using a tool like snmpwalk or similar to the Access Point controller, requesting data from OID 1.3.6.1.4.1.9.9.512.1.1.1.1.4.1. For example: snmpwalk -v 2c -c public .1.3.6.1.4.1.9.9.512.1.1.1.1.4.1
  • Scope: Cisco Access Points running software that exposes SNMP information are affected. Specific versions depend on the configuration and firmware installed.

3. Detection and Assessment

You can confirm if a system is vulnerable by checking for enabled SNMP services and accessible WLAN SSIDs. A quick check involves verifying SNMP service status, while thorough assessment requires querying the OID directly.

  • Quick checks: Use the command show running-config | include snmp to see if SNMP is configured on a Cisco device.
  • Scanning: Nessus plugin ID 10853 can detect exposed SNMP information, including WLAN SSIDs. This is an example only and may require updates.
  • Logs and evidence: Check system logs for SNMP traffic originating from unexpected sources or targeting OID 1.3.6.1.4.1.9.9.512.1.1.1.1.4.1.
show running-config | include snmp

4. Solution / Remediation Steps

The following steps outline how to fix the issue. Prioritise disabling SNMP if it is not required, or implementing strong security controls.

4.1 Preparation

  • Dependencies: Ensure you have console access to the Cisco Access Point controller in case of connectivity issues. Roll back by restoring the backed-up configuration.
  • Change window: A standard maintenance window is recommended, with approval from the IT security team.

4.2 Implementation

  1. Step 1: Disable SNMP if it’s not needed. Use the command no snmp-server community public RO to remove a default read-only community string. Repeat for other community strings.
  2. Step 2: If SNMP is required, restrict access using Access Control Lists (ACLs). Configure ACLs to allow only trusted hosts to query SNMP information. Use the command snmp-server host community public RO.
  3. Step 3: Verify that the changes have been applied by checking the running configuration again.

4.3 Config or Code Example

Before

snmp-server community public RO

After

no snmp-server community public RO

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this issue. Least privilege is key, as limiting access reduces the impact of a compromise. Input validation and safe defaults also play a role.

  • Practice 1: Implement least privilege by restricting SNMP access to only necessary hosts and users.
  • Practice 2: Use strong community strings or authentication methods for SNMP if it must be enabled.

4.5 Automation (Optional)

Ansible can automate the removal of default SNMP community strings across multiple Cisco devices.

---
- hosts: cisco_devices
  tasks:
    - name: Remove default SNMP community string
      cisco.ios.ios_config:
        lines:
          - no snmp-server community public RO
        parents: snmp-server

5. Verification / Validation

Confirm the fix by checking that the SSID is no longer accessible via SNMP and verifying core service functionality.

  • Post-fix check: Run snmpwalk -v 2c -c public .1.3.6.1.4.1.9.9.512.1.1.1.1.4.1 and confirm that the SSID is no longer returned.
  • Re-test: Repeat the initial detection method (snmpwalk) to verify the issue has been resolved.
  • Monitoring: Monitor system logs for SNMP traffic from untrusted sources as an example alert.
snmpwalk -v 2c -c public  .1.3.6.1.4.1.9.9.512.1.1.1.1.4.1

6. Preventive Measures and Monitoring

Update security baselines to include SNMP hardening guidelines, for example CIS control 5. Implement checks in CI/CD pipelines to prevent insecure configurations.

  • Baselines: Update your Cisco device security baseline to require disabling unnecessary SNMP services or enforcing strong access controls.
  • Asset and patch process: Review configurations regularly, at least quarterly, to ensure compliance with security policies.

7. Risks, Side Effects, and Roll Back

  • Risk or side effect 1: Disabling SNMP could disrupt existing network management systems. Mitigation: Plan for alternative monitoring methods.
  • Roll back: Restore the backed-up device configuration to revert any changes made.

8. References and Resources

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