How to remediate – BJNP Detection

1. Introduction

BJNP Detection indicates a printing service is listening on a remote port. This protocol, BJNP, is proprietary to Canon USB over IP network printers and can expose systems to potential risks if access isn’t controlled. Affected systems are typically those running Canon printers connected to the network. A successful exploit could lead to information disclosure or denial of service.

2. Technical Explanation

The vulnerability occurs because the remote service supports BJNP, which listens on a specific port for printing requests. An attacker can remotely connect to this port and potentially interact with the printer service. There is no known CVE associated with this detection at this time. A realistic example of exploitation involves an attacker sending malicious commands to the printer via the BJNP protocol, potentially retrieving sensitive data or disrupting print services.

• Root cause: The Canon BJNP service is enabled and listening on a network port.
• Exploit mechanism: An attacker sends crafted requests to the BJNP service over the network.
• Scope: Systems running Canon printers with the BJNP service enabled are affected.

3. Detection and Assessment

To confirm if a system is vulnerable, you can check for open ports associated with BJNP or examine printer configurations.

• Quick checks: Use netstat -an | grep (replace `` with the default BJNP port, typically 9100) to see if the service is listening.
• Scanning: Nessus plugin ID 138672 can detect BJNP services. This is an example only and may require updating.
• Logs and evidence: Check firewall logs for connections to port 9100 or other known BJNP ports.

netstat -an | grep 9100

4. Solution / Remediation Steps

To fix the issue, limit access to the port used by the BJNP service if it is not required.

4.1 Preparation

• Ensure you have a method to restore the original configuration if needed. A roll back plan involves restoring the backed-up configuration or restarting the print spooler service.
• Changes should be made during a scheduled maintenance window with appropriate approval from IT management.

4.2 Implementation

1. Step 1: Configure your firewall to block inbound connections to port 9100, unless specifically required for printing services.
2. Step 2: If the BJNP service is not needed, disable it within the printer’s configuration interface (refer to Canon documentation).

4.3 Config or Code Example

Before

# No firewall rule blocking port 9100 (example iptables)
#iptables -A INPUT -p tcp --dport 9100 -j ACCEPT

After

# Firewall rule blocking inbound connections to port 9100 (example iptables)
iptables -A INPUT -p tcp --dport 9100 -j DROP

4.4 Security Practices Relevant to This Vulnerability

List only practices that directly address this vulnerability type. Use neutral wording and examples instead of fixed advice. For example: least privilege, input validation, safe defaults, secure headers, patch cadence. If a practice does not apply, do not include it.

• Practice 1: Least privilege to reduce the attack surface by only allowing necessary network access.
• Practice 2: Network segmentation to isolate printers from critical systems and limit potential damage.

4.5 Automation (Optional)

# Example PowerShell script to block port 9100 using Windows Firewall (example only)
New-NetFirewallRule -DisplayName "Block BJNP Port" -Direction Inbound -Protocol TCP -LocalPort 9100 -Action Block

5. Verification / Validation

To confirm the fix worked, verify that connections to port 9100 are blocked and that printing services still function as expected.

• Post-fix check: Run netstat -an | grep 9100 again; it should not show the service listening on that port if blocked by a firewall.
• Re-test: Re-run the initial detection method (port scan) to confirm the port is no longer open.
• Smoke test: Print a test page to ensure printing functionality remains operational.
• Monitoring: Monitor firewall logs for any attempts to connect to port 9100, which could indicate malicious activity.

netstat -an | grep 9100 # Should return no results if blocked

6. Preventive Measures and Monitoring

Suggest only measures that are relevant to the vulnerability type. Use “for example” to keep advice conditional, not prescriptive.

• Baselines: Update security baselines or policies to include restrictions on unnecessary network services like BJNP.
• Pipelines: Implement network access control lists (ACLs) to restrict traffic to printers based on the principle of least privilege.
• Asset and patch process: Regularly review printer configurations and firmware for updates and vulnerabilities.

7. Risks, Side Effects, and Roll Back

• Risk or side effect 1: Blocking port 9100 may disrupt printing if BJNP is required for certain printer models.
• Risk or side effect 2: Incorrect firewall configuration could block legitimate network traffic.
• Roll back: Remove the firewall rule blocking port 9100, or re-enable the BJNP service in the printer’s configuration interface.

8. References and Resources

• Vendor advisory or bulletin: Refer to Canon’s support website for specific printer model documentation regarding BJNP configuration.
• NVD or CVE entry: No known CVE currently exists for this detection.
• Product or platform documentation relevant to the fix: Consult your firewall vendor’s documentation for instructions on configuring rules.