How to remediate – Detect PROFINET targets listening on the Network Layer.

1. Introduction

The vulnerability “Detect PROFINET targets listening on the Network Layer” identifies remote hosts supporting the PROFINET protocol at the network layer. This matters to businesses as it indicates potential exposure of industrial control systems (ICS) and automation devices to network-based attacks. Systems commonly affected include programmable logic controllers (PLCs), human machine interfaces (HMIs), and other PROFINET enabled equipment. A successful exploit could lead to loss of confidentiality, integrity, or availability of the ICS environment.

2. Technical Explanation

The vulnerability occurs when a device responds to a PROFINET identification Ethernet packet request. An attacker can send this request and determine if the target supports the protocol. This information gathering is the first step towards potential exploitation. There is no specific CVE associated with simply supporting the protocol, but it indicates a system requiring further security assessment. An example attack scenario involves identifying vulnerable devices on a network, then attempting to exploit known vulnerabilities in the PROFINET stack or related services.

• Root cause: The device responds to unsolicited PROFINET identification requests.
• Exploit mechanism: An attacker sends a PROFINET identification request and receives a response, confirming protocol support. This allows further reconnaissance and potential exploitation of other vulnerabilities.
• Scope: Devices supporting the PROFINET protocol on the network layer are affected.

3. Detection and Assessment

To confirm whether a system is vulnerable, first check for PROFINET services running. A thorough method involves capturing network traffic to identify PROFINET communication.

• Quick checks: Use `nmap -sV ` to scan for open ports and service versions. Look for PROFINET-related services.
• Scanning: Nessus plugin ID 16829 can detect PROFINET devices, but results should be verified manually.
• Logs and evidence: Network traffic captures using Wireshark or tcpdump may show PROFINET communication on port 65735 (default).

nmap -sV 

4. Solution / Remediation Steps

The following steps outline how to address the issue of detecting PROFINET targets listening on the Network Layer. These steps focus on network segmentation and monitoring, as direct patching may not always be available for ICS devices.

4.1 Preparation

• Services to stop: No services need to be stopped for this remediation.
• Roll back plan: Revert network segmentation rules if issues arise.

4.2 Implementation

1. Step 1: Segment the network to isolate ICS devices from untrusted networks. Use firewalls and VLANs.
2. Step 2: Implement strict firewall rules allowing only necessary PROFINET communication between trusted devices.
3. Step 3: Monitor network traffic for unexpected PROFINET communication originating from or destined to untrusted sources.

4.3 Config or Code Example

Before

# Allow all traffic on VLAN 100
access-list 100 permit any

After

# Allow only PROFINET communication (port 65735) between trusted devices on VLAN 100
access-list 100 permit tcp any host  eq 65735
access-list 100 deny ip any any

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help mitigate this vulnerability type. Network segmentation is key, as it limits the impact of compromised devices. Least privilege restricts access to only necessary resources. Continuous monitoring detects anomalous activity.

• Practice 1: Network segmentation isolates critical systems and reduces attack surface.
• Practice 2: Least privilege minimizes damage from exploited vulnerabilities.

4.5 Automation (Optional)

# Example Ansible playbook to configure firewall rules
---
- hosts: firewalls
  tasks:
    - name: Configure PROFINET firewall rule
      firewalld:
        zone: icssafetyzone
        port: 65735/tcp
        permanent: true
        state: enabled

5. Verification / Validation

Confirm the fix by verifying network segmentation rules and re-scanning for open PROFINET ports from untrusted networks. Perform a service smoke test to ensure legitimate communication is not blocked.

• Post-fix check: Use `nmap -sV ` from an untrusted network; no PROFINET services should be visible.
• Re-test: Re-run the initial `nmap` scan to confirm that PROFINET ports are not accessible from outside the segmented network.
• Smoke test: Verify that authorized devices can still communicate using PROFINET.

nmap -sV 

6. Preventive Measures and Monitoring

Update security baselines to include network segmentation requirements for ICS environments. Implement intrusion detection systems (IDS) to monitor for anomalous PROFINET traffic. Regular patch reviews are essential, though often challenging in ICS deployments.

• Baselines: Update a security baseline or policy to require network segmentation for all ICS devices.
• Asset and patch process: Establish a regular review cycle for firmware updates and security patches, even if implementation is delayed.

7. Risks, Side Effects, and Roll Back

Network segmentation may disrupt existing communication paths. Incorrect firewall rules can block legitimate traffic. Roll back by reverting the network configuration to its previous state.

• Risk or side effect 1: Disruption of existing PROFINET communication if rules are too restrictive.
• Risk or side effect 2: Blocking legitimate services due to misconfigured firewall rules.
• Roll back: Revert the network configuration changes made in steps 1 and 2. Restore previous firewall rules.

8. References and Resources

• Vendor advisory or bulletin: https://www.profibus.com/technology/profinet/