How to remediate – DNS Server hostname.bind Map Hostname Disclosure

1. Introduction

The DNS Server hostname.bind Map Hostname Disclosure vulnerability allows an attacker to learn the remote host name by querying the DNS server for ‘hostname.bind’ in the CHAOS domain. This can reveal internal system names, potentially aiding reconnaissance efforts and increasing the risk of targeted attacks. Systems running a vulnerable DNS server are affected. A successful exploit could lead to information disclosure.

2. Technical Explanation

The vulnerability occurs because some DNS servers respond to queries for ‘hostname.bind’ in the CHAOS domain, revealing the remote host name. This is an intentional feature of older DNS implementations but presents a security risk in modern environments. An attacker can simply query the DNS server to obtain this information. There is no CVE associated with this specific disclosure; however, it relates to the general functionality of hostname resolution.

• Root cause: The DNS server unnecessarily responds to queries for ‘hostname.bind’ in the CHAOS domain.
• Exploit mechanism: An attacker sends a DNS query for ‘hostname.bind’ and receives a response containing the remote host name. For example, using `nslookup hostname.bind chaos`.
• Scope: All DNS servers that have not disabled this feature are affected. This includes BIND, Microsoft DNS Server, and other implementations.

3. Detection and Assessment

You can confirm if a system is vulnerable by querying the DNS server for ‘hostname.bind’. A thorough method involves monitoring DNS query logs for requests to the CHAOS domain.

• Quick checks: Use `nslookup hostname.bind chaos` from a command prompt or terminal. If the remote host name is returned, the system is vulnerable.
• Scanning: Nmap can be used with the dns-brute script to identify DNS servers responding to ‘hostname.bind’ queries. Example: `nmap -p 53 –script dns-brute `.
• Logs and evidence: Check DNS server logs for queries containing “hostname.bind” or originating from the CHAOS domain (e.g., `chaos` TLD). The exact log location varies depending on the DNS server software.

nslookup hostname.bind chaos

4. Solution / Remediation Steps

The solution is to disable the feature that responds to ‘hostname.bind’ queries. Consult your vendor’s documentation for specific instructions.

4.1 Preparation

• Ensure you have access to the DNS server configuration files and appropriate permissions. A roll back plan involves restoring the snapshot or reverting the configuration change.
• A planned maintenance window may be needed, depending on the impact of stopping the DNS service. Approval from a system administrator is recommended.

4.2 Implementation

1. Step 1: Consult your DNS server documentation for instructions on disabling hostname.bind responses.
2. Step 2: Modify the DNS server configuration file to disable this feature. The specific setting varies by vendor (e.g., in BIND, you may need to adjust options related to CHAOS domain queries).
3. Step 3: Restart the DNS service for the changes to take effect.

4.3 Config or Code Example

Before

//Example BIND configuration (may vary)
options {
    allow-transfer { none; };
};

After

//Example BIND configuration (may vary)
options {
    allow-transfer { none; };
    dnssec-validation auto; // Add this line to disable hostname.bind responses
};

4.4 Security Practices Relevant to This Vulnerability

Least privilege can reduce the impact if exploited, as attackers will have limited access to internal system information. Regular security audits and configuration reviews help identify and address unnecessary features like this one.

• Practice 1: Least privilege – limit access to DNS server configurations to authorized personnel only.
• Practice 2: Configuration review – regularly audit DNS server settings for unnecessary or insecure options.

4.5 Automation (Optional)

Automation is not generally recommended for this specific vulnerability due to the vendor-specific configuration changes required. However, infrastructure-as-code tools can be used to manage DNS configurations consistently and enforce security baselines.

# Example Ansible task (may vary significantly depending on your environment)
- name: Disable hostname.bind responses in BIND
  lineinfile:
    path: /etc/named.conf
    regexp: '^options {'
    insertafter: 'allow-transfer { none; };'
    line: 'dnssec-validation auto;'
  notify: Restart DNS service

5. Verification / Validation

• Post-fix check: Run `nslookup hostname.bind chaos`. If no response or an error is returned, the fix is successful.
• Re-test: Repeat the initial detection method (nslookup) to confirm that the vulnerability is resolved.
• Monitoring: Monitor DNS server logs for any unexpected errors or changes in behavior following the configuration update. Example query: search logs for “hostname.bind” to ensure no responses are being sent.

nslookup hostname.bind chaos

6. Preventive Measures and Monitoring

Update security baselines to include disabling unnecessary DNS features. Implement regular configuration reviews as part of your patch management process.

• Baselines: Update a security baseline or policy (e.g., CIS control 10.2) to require disabling hostname.bind responses on all DNS servers.
• Asset and patch process: Review DNS server configurations during regular asset audits or as part of a vulnerability management program. A review cycle of every 6 months is sensible.

7. Risks, Side Effects, and Roll Back

• Risk or side effect 1: Incorrectly configured DNS settings can cause service outages. Mitigation: Test changes in a non-production environment first.
• Roll back: Restore the DNS server from the pre-change snapshot. Alternatively, revert the modifications made to the configuration file and restart the DNS service.

8. References and Resources

• Vendor advisory or bulletin: Consult your DNS server vendor’s documentation for specific instructions on disabling hostname.bind responses.
• NVD or CVE entry: No specific CVE is associated with this disclosure, but information can be found regarding the general functionality of hostname resolution.
• Product or platform documentation relevant to the fix: BIND documentation: [https://www.isc.org/docs/bind9/options.html](https://www.isc.org/docs/bind9/options.html)