How to remediate – Well-known SSL Certificate Used in Remote Device

1. Introduction

The vulnerability, Well-known SSL Certificate Used in Remote Device, means a remote service is using an SSL certificate whose private key is publicly available. This allows attackers to decrypt communications with the service. Systems commonly affected are embedded devices, IoT equipment and older servers that ship with default certificates. Confidentiality of data transmitted between clients and the remote host is at high risk.

2. Technical Explanation

The root cause is the use of a default SSL certificate provided by the device manufacturer or service provider, where the corresponding private key has been published online. An attacker can intercept network traffic and decrypt communications because they possess the private key. Exploitation requires an ability to passively monitor network traffic between clients and the vulnerable host.

• Root cause: Shipping with a default SSL certificate and publicly available private key.
• Exploit mechanism: An attacker intercepts encrypted traffic using tools like Wireshark, then uses the published private key to decrypt it. For example, an attacker monitoring network traffic from a smart thermostat could read user credentials or control commands.
• Scope: Embedded devices, IoT equipment, and older servers are affected. Specific versions depend on the vendor’s default configuration.

3. Detection and Assessment

You can confirm vulnerability by checking the certificate details of the remote service. A quick check is to examine the certificate chain using a web browser or command-line tool. A thorough method involves analysing the certificate with OpenSSL.

• Quick checks: Use a web browser to connect to the service and view the certificate information. Look for certificates issued by known default authorities.
• Scanning: Nessus plugin ID 10384 can identify well-known SSL certificates, but results should be manually verified.
• Logs and evidence: Examine server logs for certificate issuance or renewal events. Check configuration files for the certificate path.

openssl s_client -connect targethost:443 | openssl x509 -noout -text

4. Solution / Remediation Steps

Replace the default SSL certificate with a properly generated or purchased one. This ensures secure communications and prevents decryption of traffic.

4.1 Preparation

• Ensure you have access to a Certificate Authority (CA) or the ability to generate a self-signed certificate. A roll back plan is to restore the original configuration from the backup.
• A change window may be needed, depending on service criticality. Approval should come from the system owner.

4.2 Implementation

1. Step 1: Purchase a new SSL certificate from a trusted CA or generate a self-signed certificate using OpenSSL.
2. Step 2: Stop the affected service on the remote host.
3. Step 3: Replace the existing default certificate with the new certificate and its private key in the appropriate configuration file.
4. Step 4: Restart the affected service.

4.3 Config or Code Example

Before

# Example Apache configuration using default certificate
SSLCertificateFile /etc/ssl/certs/default.pem
SSLCertificateKeyFile /etc/ssl/private/default.key

After

# Example Apache configuration with new certificate
SSLCertificateFile /etc/ssl/certs/new_certificate.pem
SSLCertificateKeyFile /etc/ssl/private/new_certificate.key

4.4 Security Practices Relevant to This Vulnerability

Several security practices can prevent this issue. Least privilege limits the impact of a compromised certificate. Secure defaults ensure systems start with strong configurations.

• Practice 1: Implement least privilege access controls to limit who can manage certificates and keys.
• Practice 2: Enforce secure defaults by requiring custom certificates during device provisioning or service setup.

4.5 Automation (Optional)

# Example Ansible playbook snippet for certificate replacement
- name: Replace SSL Certificate
  copy:
    src: /path/to/new_certificate.pem
    dest: /etc/ssl/certs/new_certificate.pem
    owner: root
    group: root
    mode: 0644
  notify: Restart service

5. Verification / Validation

Confirm the fix by verifying the new certificate is in use and that the old certificate is no longer present. Check network traffic to ensure it’s encrypted with the correct certificate.

• Post-fix check: Use `openssl s_client -connect targethost:443 | openssl x509 -noout -text` and confirm the output shows the new certificate details.
• Re-test: Re-run the earlier detection method to verify the well-known certificate is no longer present.
• Smoke test: Verify users can still connect to the service without errors. Test key functionality, such as login or data transfer.
• Monitoring: Monitor server logs for certificate renewal failures or unexpected SSL errors.

openssl s_client -connect targethost:443 | openssl x509 -noout -text

6. Preventive Measures and Monitoring

Update security baselines to require custom certificates, and add checks in CI/CD pipelines to prevent default certificates from being deployed. A regular patch cycle ensures timely updates.

• Baselines: Update your security baseline or policy to mandate the use of properly generated SSL certificates for all services.
• Asset and patch process: Implement a regular review cycle for server configurations, including certificate validity and key management practices.

7. Risks, Side Effects, and Roll Back

Replacing the SSL certificate may cause temporary service disruption if misconfigured. Incorrect configuration can lead to connection errors. A roll back involves restoring the original configuration from the backup.

• Risk or side effect 2: Connection errors if the new certificate chain is not trusted by clients. Mitigation is ensuring a valid and properly configured CA.
• Roll back: 1) Stop the affected service. 2) Restore the original configuration files from backup. 3) Restart the service.

8. References and Resources

• Vendor advisory or bulletin: http://www.devttys0.com/2010/12/breaking-ssl-on-embedded-devices/
• NVD or CVE entry: No specific CVE is listed for this general issue, but related vulnerabilities may exist depending on the affected product.
• Product or platform documentation relevant to the fix: Refer to your vendor’s documentation for instructions on certificate replacement and key management.