How to remediate – XOT Detection

1. Introduction

The XOT Detection plugin identifies systems running X.25 over TCP, known as XOT. This protocol is outdated and rarely used legitimately, making any instance a potential security risk. Businesses should be aware of this because XOT routers may have unpatched vulnerabilities or weak configurations. A successful attack could compromise confidentiality, integrity, and availability of network communications.

2. Technical Explanation

XOT is an encapsulation of the X.25 protocol over TCP/IP. It was used to connect older networks to modern IP-based infrastructure. The remote target being identified as an XOT router indicates it’s actively listening for and processing X.25 packets over a TCP connection. Exploitation typically involves sending crafted X.25 packets to trigger buffer overflows or other vulnerabilities within the router’s XOT stack.

• Root cause: The presence of an active XOT service, which is inherently insecure due to its age and lack of modern security features.
• Exploit mechanism: An attacker could send a malicious X.25 packet designed to overflow a buffer in the router’s XOT processing logic, potentially gaining remote code execution.
• Scope: Cisco routers are commonly affected by this issue, particularly older models that still support X.25 functionality.

3. Detection and Assessment

Confirming an XOT service is running can be done quickly using network scanning tools or by examining the router’s configuration. A thorough assessment involves analysing traffic patterns to identify X.25 packets.

• Quick checks: Use netstat -an | grep :21 to check for listening services on port 21, a common XOT port.
• Scanning: Nmap can detect XOT with the script nmap --script x25 (example only).
• Logs and evidence: Check router logs for messages related to X.25 or PPP connections. Specific log file locations vary by vendor.

netstat -an | grep :21

4. Solution / Remediation Steps

The best solution is to disable the XOT service if it’s not required. If XOT is essential, ensure the router firmware is up-to-date and properly configured.

4.1 Preparation

• Ensure you have console access or another reliable method for restoring the configuration if needed. A roll back plan involves reverting to the previous configuration file.
• A change window may be required depending on your network’s criticality and impact of service interruption. Approval from a senior network engineer is recommended.

4.2 Implementation

1. Step 1: Log in to the router’s command-line interface.
2. Step 2: Enter configuration mode.
3. Step 3: Disable the XOT service using the appropriate command (e.g., no x25 or similar, depending on your router model).
4. Step 4: Save the configuration.

4.3 Config or Code Example

Before

interface Serial0/0/0
 ip address 192.168.1.1 255.255.255.0
 x25 enable

After

interface Serial0/0/0
 ip address 192.168.1.1 255.255.255.0
 no x25

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help mitigate the risks associated with outdated protocols like XOT. Least privilege reduces impact if exploited, and a strong patch cadence ensures timely updates for known vulnerabilities.

• Practice 1: Least privilege – limit access to network devices to only those who require it.
• Practice 2: Patch cadence – regularly update router firmware to address security vulnerabilities.

4.5 Automation (Optional)

# Example Ansible playbook snippet (use with caution)
- name: Disable XOT service on Cisco routers
  cisco.ios.ios_config:
    lines:
      - no x25
    parents: interface Serial0/0/0 # Adjust interface as needed
  become: yes

5. Verification / Validation

Confirm the fix by checking that the XOT service is no longer listening on port 21 and re-running the initial detection methods. A simple smoke test involves verifying basic network connectivity.

• Post-fix check: Run netstat -an | grep :21; there should be no output indicating a listener on port 21.
• Re-test: Re-run the Nmap scan (nmap --script x25 ) and confirm it does not detect XOT.
• Smoke test: Ping a known host on the network to verify basic connectivity is still functioning.
• Monitoring: Monitor router logs for any unexpected X.25-related messages (example only).

netstat -an | grep :21

6. Preventive Measures and Monitoring

Update security baselines to explicitly prohibit the use of outdated protocols like XOT. Implement checks in CI/CD pipelines to prevent configurations with XOT enabled from being deployed. A sensible patch review cycle should be established based on risk assessment.

• Baselines: Update your network device baseline configuration to disable XOT by default.
• Pipelines: Add a check to your CI/CD pipeline that flags any router configurations with the XOT service enabled.
• Asset and patch process: Review router configurations quarterly for compliance with security baselines.

7. Risks, Side Effects, and Roll Back

• Roll back: Restore the previous router configuration file to re-enable the XOT service.

8. References and Resources

• Vendor advisory or bulletin: http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/x25.pdf
• NVD or CVE entry: Not applicable for this information vulnerability.
• Product or platform documentation relevant to the fix: http://www.ietf.org/rfc/rfc1613.txt