CAM Table Attack: 2011 Mitigation

TL;DR

The 2011 CAM table attack exploited vulnerabilities in network switches to redirect traffic. This guide outlines steps to identify if your systems were affected and how to mitigate the risk, focusing on firmware updates, port security, and monitoring.

Understanding the Attack

In 2011, a significant vulnerability was discovered affecting many Cisco network switches (and potentially others). Attackers could flood the switch’s Content Addressable Memory (CAM) table with bogus MAC addresses. This overwhelmed the CAM table, causing it to malfunction and effectively turn the switch into a hub – broadcasting all traffic instead of forwarding it selectively. This allowed attackers to sniff sensitive data.

Step 1: Identify Affected Devices

1. Inventory your network switches: Create a list of all network switches, including make and model numbers.
2. Check vendor advisories: Visit the websites of your switch manufacturers (e.g., Cisco) and search for security advisories related to CAM table attacks or MAC flooding vulnerabilities from 2011-2012. Specifically look for CVE-2011-3698, CVE-2011-4756, and similar entries.
3. Determine firmware versions: Log into each switch’s management interface (usually via a web browser or SSH) and record the current firmware version. Compare this against the vendor’s advisory to see if your device is running a vulnerable version.

Step 2: Apply Firmware Updates

The primary mitigation for this attack is applying the security patches released by your switch vendors.

1. Download the correct firmware: Obtain the latest, recommended firmware version from your vendor’s support website. Ensure it’s specifically designed for your switch model.
2. Backup your configuration: Before updating any firmware, create a complete backup of the switch’s current configuration. This allows you to restore settings if something goes wrong during the update process. Most switches have a command like

   show running-config

   which can be saved to a file.

3. Perform the upgrade: Follow your vendor’s instructions for upgrading the firmware. This usually involves uploading the new firmware image via TFTP or SCP and then activating it. Do not interrupt the process!
4. Verify the update: After the upgrade, verify that the correct firmware version is installed by checking the switch’s management interface again.

Step 3: Implement Port Security

Port security limits the number of MAC addresses allowed on each port, preventing attackers from flooding the CAM table.

1. Enable port security: Access your switch’s configuration interface.
2. Configure maximum MAC addresses: Set a limit on the number of MAC addresses permitted per port (e.g., 1 or 2). This depends on how many devices you expect to connect to each port. Use commands like these (Cisco example):

   interface GigabitEthernet0/1
    switchport mode access
    switchport port-security maximum 1
    switchport port-security mac-address sticky

3. Configure violation actions: Determine what happens when a port security violation occurs. Options include shutting down the port, logging the event, or sending an SNMP trap.

   switchport port-security violation restrict

4. Apply to all relevant ports: Repeat these steps for all access ports on your switches. Avoid enabling port security on trunk ports.

Step 4: Monitor Network Traffic

Regular monitoring can help detect suspicious activity related to MAC flooding or unusual traffic patterns.

1. Enable logging: Ensure that your switches are configured to log security events, including port security violations and excessive broadcast traffic.
2. Monitor CPU usage: High CPU utilization on a switch can indicate it’s struggling with a CAM table overflow.
3. Look for unusual broadcasts: Use network monitoring tools (e.g., Wireshark) to analyze traffic patterns and identify an excessive number of broadcast packets.
4. Consider intrusion detection/prevention systems (IDS/IPS): Implement IDS/IPS solutions that can detect MAC flooding attacks in real-time.

Step 5: Review Switch Configurations

Regularly review your switch configurations to ensure port security settings are still appropriate and haven’t been inadvertently changed.

1. Document changes: Keep a record of all configuration changes made to your switches.
2. Automate where possible: Use network automation tools to enforce consistent configurations across all devices.