How to remediate – RPC bootparamd NIS Domain Name Disclosure

1. Introduction

The RPC bootparamd NIS Domain Name Disclosure vulnerability allows an attacker to obtain information about a network’s NIS domain from the remote bootparamd service. This can provide attackers with valuable reconnaissance data for further attacks against systems on the network. Systems running the bootparamd service are usually affected, particularly those using Network Information Service (NIS). A successful exploit could lead to compromised confidentiality of network details.

2. Technical Explanation

The vulnerability occurs because the RPC bootparamd service unintentionally discloses the NIS domain name during communication. An attacker can query the service and retrieve this information without authentication. This is a remote issue, meaning an attacker does not need local access to exploit it. While no specific CVE exists for this precise disclosure, similar issues have been documented relating to insecure RPC configurations.

• Root cause: The bootparamd service lacks sufficient controls over the data it exposes via the RPC interface.
• Exploit mechanism: An attacker sends a request to the bootparamd service and parses the response for the NIS domain name. For example, using an RPC client tool like rpcclient.
• Scope: Affected platforms include systems running Linux, Unix, and potentially older Windows versions with NIS enabled. Specific versions depend on the implementation of the bootparamd service.

3. Detection and Assessment

You can confirm if a system is vulnerable by checking for the presence of the bootparamd service and attempting to retrieve its configuration information. A thorough method involves network traffic analysis.

• Quick checks: Use systemctl status bootparamd on Linux systems to check if the service is running.
• Scanning: Nessus plugin ID 10387 can identify this issue, but results should be verified manually.
• Logs and evidence: Examine system logs for RPC communication related to bootparamd. Look for entries indicating domain name exposure.

systemctl status bootparamd

4. Solution / Remediation Steps

The primary solution is to filter incoming traffic to the port used by the bootparamd service, preventing external access. Only allow trusted hosts to connect.

4.1 Preparation

• Ensure you have network firewall rules in place for roll back. A roll back plan involves reverting the firewall rule change.
• Change windows may be needed depending on your environment and approval processes.

4.2 Implementation

1. Step 1: Identify the port used by bootparamd (typically TCP/UDP port 111).
2. Step 2: Configure your firewall to block incoming traffic to this port, except from trusted sources. For example, using iptables on Linux.
3. Step 3: Restart the firewall service to apply the changes.

4.3 Config or Code Example

Before

# No specific rule blocking bootparamd port 111

After

iptables -A INPUT -p tcp --dport 111 -j DROP

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this type of issue. Least privilege reduces the impact if exploited, and network segmentation limits exposure.

• Practice 1: Implement least privilege by restricting access to services like bootparamd only to authorized hosts.
• Practice 2: Network segmentation isolates vulnerable services from critical systems.

4.5 Automation (Optional)

# Example Ansible playbook snippet to block port 111 with firewalld
- name: Block bootparamd port
  firewalld:
    port: 111/tcp
    permanent: true
    state: disabled
    immediate: yes

5. Verification / Validation

• Post-fix check: Run rpcclient -T and verify that you cannot query the bootparamd service or obtain the NIS domain name.
• Re-test: Re-run the earlier detection method (systemctl status bootparamd) to confirm the service is still running but inaccessible from external networks.
• Monitoring: Monitor firewall logs for blocked connections to port 111, indicating attempted exploitation.

rpcclient -T 

6. Preventive Measures and Monitoring

Update security baselines to include restrictions on RPC services like bootparamd. Implement regular vulnerability scanning in your CI/CD pipelines.

• Baselines: Update a security baseline or policy (for example, CIS control 5) to require restricted access for RPC services.
• Pipelines: Add checks in CI or deployment pipelines to scan for insecure configurations like open ports on bootparamd.
• Asset and patch process: Implement a regular review cycle of system configurations to identify and address potential vulnerabilities.

7. Risks, Side Effects, and Roll Back

Blocking port 111 may disrupt legitimate services relying on RPC communication. A roll back involves removing the firewall rule.

• Roll back: Step 1: Remove the iptables rule using iptables -D INPUT -p tcp --dport 111 -j DROP. Step 2: Restart the firewall service.

8. References and Resources

• Vendor advisory or bulletin: No specific vendor advisory available for this precise disclosure, but check your OS vendor’s security pages.
• NVD or CVE entry: No direct CVE exists, but search NVD for similar RPC-related vulnerabilities.
• Product or platform documentation relevant to the fix: Refer to your operating system’s firewall configuration documentation (e.g., iptables man page).