How to remediate – Oracle TNS Listener VSNNUM Version Remote Information Disclosure

1. Introduction

Oracle TNS Listener VSNNUM Version Remote Information Disclosure allows an unauthenticated user to extract the version number of a remote Oracle TNS listener service. This could aid attackers in identifying vulnerable systems and planning further attacks. Systems running Oracle databases with exposed TNS listeners are typically affected, impacting confidentiality through information leakage.

2. Technical Explanation

The vulnerability occurs because the TNS listener responds to unauthenticated requests with its version number. An attacker can simply connect to the port used by the TNS listener and request this information. This does not necessarily indicate a weakness in the database itself, but reveals details about the infrastructure. There is no known CVE associated with this specific disclosure, however similar issues are tracked under CWE-200: Exposure of Sensitive Information.

• Root cause: The TNS listener service provides version information without authentication.
• Exploit mechanism: An attacker connects to the TNS port (typically 1521) and sends a request that elicits the version response. For example, using netcat: nc 1521 followed by observing the banner output.
• Scope: Oracle databases running with an exposed TNS listener service are affected. Specific versions of the listener may be more or less verbose in their responses.

3. Detection and Assessment

You can confirm a system is vulnerable by checking for a response from the TNS port. A thorough assessment involves identifying all systems with exposed TNS listeners.

• Quick checks: Use netcat to connect to port 1521 on potential Oracle database servers and observe the banner output.
• Scanning: Nessus plugin ID 38764 can identify this vulnerability, but results should be manually verified.
• Logs and evidence: Review firewall logs for connections to port 1521 from unexpected sources.

nc  1521

4. Solution / Remediation Steps

Restrict access to the database to only allowed IP addresses. This prevents unauthenticated users from querying the TNS listener version.

4.1 Preparation

• Ensure you have access to the firewall configuration and can revert changes if needed. A roll back plan is to restore from the snapshot or re-open port 1521 to all IPs.
• A change window may be required depending on your organisation’s policies, with approval from the database administrator.

4.2 Implementation

1. Step 1: Configure the firewall to allow connections to port 1521 only from trusted IP addresses or networks.
2. Step 2: Verify that connections from untrusted sources are blocked.

4.3 Config or Code Example

Before

# Allow all connections to port 1521 (example using iptables)
iptables -A INPUT -p tcp --dport 1521 -j ACCEPT

After

# Allow only specific IP address to connect to port 1521 (example using iptables)
iptables -A INPUT -s /32 -p tcp --dport 1521 -j ACCEPT
iptables -A INPUT -p tcp --dport 1521 -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.

• Practice 1: Least privilege network access reduces the attack surface by limiting who can connect to sensitive services.

4.5 Automation (Optional)

# Example Ansible playbook to restrict TNS listener access
---
- hosts: all
  tasks:
    - name: Restrict access to port 1521
      iptables:
        chain: INPUT
        protocol: tcp
        dport: 1521
        source: /32
        jump: ACCEPT
    - name: Drop all other connections to port 1521
      iptables:
        chain: INPUT
        protocol: tcp
        dport: 1521
        jump: DROP

5. Verification / Validation

Confirm the fix by attempting a connection from an untrusted source and verifying it is blocked.

• Post-fix check: Use netcat to connect to port 1521 from an untrusted IP address. The connection should be refused or time out.
• Re-test: Repeat the initial netcat test from a non-trusted source, confirming no banner is received.
• Smoke test: Verify that legitimate database connections from trusted sources still function correctly.
• Monitoring: Monitor firewall logs for blocked connection attempts to port 1521 from unexpected IPs.

nc  1521 # Should timeout or be refused

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 your network security baseline to include restrictions on access to database ports like 1521.
• Pipelines: Implement infrastructure-as-code scanning to identify open ports and ensure firewall rules are correctly configured.
• Asset and patch process: Regularly review asset inventories to identify systems running Oracle databases with exposed TNS listeners.

7. Risks, Side Effects, and Roll Back

• Roll back: Remove the firewall rules added in Step 1, restoring access to port 1521 from all sources.

8. References and Resources

• Vendor advisory or bulletin: No specific advisory available for this information disclosure, refer to Oracle’s general security best practices.
• NVD or CVE entry: Not applicable as there is no associated CVE.
• Product or platform documentation relevant to the fix: Oracle Net Listener Configuration