How to remediate – TLS Version 1.1 Protocol Detection (PCI DSS)

1. Introduction

The TLS Version 1.1 Protocol Detection vulnerability concerns the use of an outdated and insecure encryption protocol, TLS 1.1. This affects services that accept connections using this protocol, potentially allowing attackers to intercept sensitive data. Systems commonly affected include web servers, email servers, and any application communicating over HTTPS or other TLS-based protocols. A successful exploit could compromise confidentiality, integrity, and availability of communications.

2. Technical Explanation

The vulnerability arises from known cryptographic flaws within the TLS 1.1 protocol itself. Attackers can leverage these weaknesses to conduct man-in-the-middle attacks or decrypt communication sessions. Exploitation requires a network connection to an affected service supporting TLS 1.1. No specific CVE is mentioned in the provided context, but multiple cryptographic flaws are known to exist within this version of TLS.

• Root cause: The remote service continues to support the outdated and vulnerable TLS 1.1 protocol.
• Exploit mechanism: An attacker can intercept traffic negotiated using TLS 1.1 and attempt to decrypt it, or perform a man-in-the-middle attack by downgrading the connection to TLS 1.1 if possible.
• Scope: Any service accepting connections encrypted with TLS 1.1 is affected. This includes web servers (Apache, Nginx, IIS), email servers, and other applications using TLS for communication.

3. Detection and Assessment

Confirming vulnerability involves checking the TLS versions supported by a service. A quick check can be done via command line tools. Thorough assessment requires scanning with dedicated security tools.

• Quick checks: Use `openssl s_client -connect : -tls1_1` to attempt a connection using TLS 1.1. If successful, the service is vulnerable.
• Scanning: Nessus plugin ID 64859 or Qualys SSL Labs scan can identify services supporting TLS 1.1. These are examples only.
• Logs and evidence: Check server logs for TLS version negotiation details. Look for entries indicating successful TLS 1.1 handshakes. Specific log file locations vary by service (e.g., Apache access logs, IIS logs).

openssl s_client -connect example.com:443 -tls1_1

4. Solution / Remediation Steps

The solution requires disabling TLS 1.1 and enabling TLS 1.2 or greater on all affected systems. This must be completed by June 2018, as per PCI DSS requirements.

4.1 Preparation

• Services: Stop and start the web service or application to ensure changes take effect.
• Dependencies: Ensure all third-party entities (Acquirers, Processors, Gateways, Service Providers) also support TLS 1.2 or greater. A roll back plan involves restoring the original server configuration from backup.

4.2 Implementation

1. Step 1: Update the web server configuration to disable TLS 1.1 and enable TLS 1.2 or higher.
2. Step 2: Restart the web service or application for changes to take effect.
3. Step 3: Verify that TLS 1.1 is no longer supported (see Verification section).

4.3 Config or Code Example

Before

SSLProtocol all -SSLv3

After

SSLProtocol All -TLSv1 -TLSv1.1 -SSLv3

4.4 Security Practices Relevant to This Vulnerability

Several security practices help prevent this type of vulnerability.

• Practice 1: Patch cadence – Regularly apply security updates to all systems, including web servers and applications.
• Practice 2: Secure defaults – Configure services with the most secure settings by default, disabling outdated protocols like TLS 1.1.

4.5 Automation (Optional)

No automation script is provided in the context.

5. Verification / Validation

Verification involves confirming that TLS 1.1 is disabled and TLS 1.2 or greater is enabled.

• Post-fix check: Use `openssl s_client -connect : -tls1_1` again. The connection should now fail.
• Re-test: Re-run the Nessus scan or Qualys SSL Labs scan to confirm TLS 1.1 is no longer reported as supported.
• Smoke test: Verify that users can still access the website and perform key functions (e.g., login, checkout).
• Monitoring: Monitor server logs for any errors related to TLS connections. Look for failed handshake attempts using TLS 1.1.

openssl s_client -connect example.com:443 -tls1_1

6. Preventive Measures and Monitoring

Preventive measures include updating security baselines and incorporating checks into deployment pipelines.

• Baselines: Update your server security baseline to explicitly disable TLS 1.1 and require TLS 1.2 or greater.
• Pipelines: Add a check in your CI/CD pipeline to verify that new deployments do not enable TLS 1.1.
• Asset and patch process: Implement a regular patch review cycle for all systems, including web servers and applications.

7. Risks, Side Effects, and Roll Back

Disabling TLS 1.1 may cause compatibility issues with older clients. A roll back plan is essential.

• Risk or side effect 1: Older clients using only TLS 1.0 or earlier may be unable to connect.
• Risk or side effect 2: Potential service interruption if the configuration change introduces errors.
• Roll back: Restore the original server configuration from backup. Restart the web service or application.

8. References and Resources

Links only to sources that match this exact vulnerability.

• Vendor advisory or bulletin: No link provided in context.
• NVD or CVE entry: No link provided in context.
• Product or platform documentation relevant to the fix: No link provided in context.