How to remediate – SSL Certificate Chain Contains Illegitimate TURKTRUST Intermed…

1. Introduction

The SSL Certificate Chain Contains Illegitimate TURKTRUST Intermediate… vulnerability means a service’s certificate chain includes an intermediate certificate authority issued by TURKTRUST that is not trusted by common operating systems and software. This can allow attackers to intercept encrypted communications, potentially stealing sensitive data. Systems using TLS/SSL with affected certificates are at risk, particularly public-facing web servers and email services. Impact on confidentiality is likely high if exploited; integrity and availability could be impacted depending on the attacker’s goals.

2. Technical Explanation

The vulnerability occurs because of an accidental issuance of intermediate CAs by TURKTRUST that were not widely distributed or trusted. When a client connects to a service using a certificate chain signed by one of these illegitimate CAs, the client cannot verify the authenticity of the certificate and may display warnings or allow an attacker to perform a man-in-the-middle attack. Exploitation requires a vulnerable system attempting to establish a TLS/SSL connection with a server presenting a certificate chain containing the untrusted TURKTRUST intermediate CA.

• Root cause: The X.509 certificate chain sent by the remote host contains an intermediate Certificate Authority (CA) that was accidentally issued by TURKTRUST and is not trusted by default in common trust stores.
• Exploit mechanism: An attacker could intercept TLS/SSL traffic between a client and server, presenting their own certificate signed by the illegitimate CA. The client may accept this certificate if it lacks awareness of the untrusted intermediate authority, allowing the attacker to decrypt and modify the communication.
• Scope: Systems using TLS/SSL with certificates chained to an intermediate CA issued by TURKTRUST are affected. This includes web servers (Apache, Nginx, IIS), email servers, VPN gateways, and any application relying on SSL/TLS for secure communication.

3. Detection and Assessment

To confirm vulnerability, check the certificate chain presented by the service. A quick check involves examining the certificate details in a web browser or using command-line tools. Thorough assessment requires analysing the full certificate chain to identify any untrusted intermediate CAs.

• Quick checks: Use a web browser to connect to the affected service and view the certificate details. Look for certificates issued by TURKTRUST as an intermediate authority.
• Scanning: Nessus plugins 28f2792 and d92931ec may identify this vulnerability. These are examples only, and results should be verified manually.
• Logs and evidence: Examine SSL/TLS handshake logs for certificate chain details. Look for entries containing TURKTRUST intermediate CA certificates. Specific log file locations vary depending on the server software (e.g., Apache access logs, IIS logs).

openssl s_client -connect example.com:443 2>/dev/null | openssl x509 -noout -text

4. Solution / Remediation Steps

The solution involves ensuring that software and operating systems blacklist the problematic intermediate CAs issued by TURKTRUST. This prevents clients from trusting certificates chained to these untrusted authorities.

4.1 Preparation

• Ensure you have a tested rollback plan in case of issues. Reverting to the original certificate chain is usually sufficient.
• Changes should be approved by a senior administrator or security team member.

4.2 Implementation

1. Step 1: Update your operating system’s trust store with the latest root and intermediate CA certificates. This may involve running system updates (e.g., `apt update && apt upgrade` on Debian/Ubuntu, or Windows Updates).
2. Step 2: Configure your web server or application to explicitly distrust the problematic TURKTRUST intermediate CAs if they are not automatically blacklisted by the operating system.
3. Step 3: Restart affected services to apply the changes.

4.3 Config or Code Example

Before

# No specific configuration for distrusting TURKTRUST intermediate CAs

After

# Example Apache configuration (may vary depending on your setup)
SSLCAFile /etc/ssl/certs/trusted-ca-bundle.pem #Ensure the bundle is up to date

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. If a practice does not apply, do not include it.

• Practice 1: Maintain a regular patch cadence for your operating systems and software to ensure the latest root CA certificates are installed.
• Practice 2: Implement certificate pinning where appropriate to restrict which CAs are trusted for specific services.

4.5 Automation (Optional)

# Example PowerShell script to update root CA certificates on Windows servers
# Requires administrator privileges
Import-Module PKI
Get-RootCAStore -Location Cert:LocalMachineMy | Update-RootCAStore #This will attempt to update the trust store automatically. Review output for errors.

5. Verification / Validation

Confirm the fix by verifying that the problematic TURKTRUST intermediate CA is no longer trusted by the system. Re-run the earlier detection methods and ensure they no longer report the vulnerability. Perform a simple service smoke test to confirm functionality remains unaffected.

• Post-fix check: Run `openssl s_client -connect example.com:443 2>/dev/null | openssl x509 -noout -text` and verify that the certificate chain does not include the untrusted TURKTRUST intermediate CA.
• Re-test: Re-run the web browser check from step 3 of Detection and Assessment. The browser should no longer display warnings related to the untrusted certificate.
• Smoke test: Access key website pages or services that rely on TLS/SSL to confirm they are still functioning correctly.
• Monitoring: Monitor SSL/TLS handshake logs for any errors related to certificate validation failures. Look for events indicating untrusted certificates.

openssl s_client -connect example.com:443 2>/dev/null | openssl x509 -noout -text #Should not show TURKTRUST intermediate CA

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 security baseline or policy to require regular updates of root CA certificates (for example, using a CIS control).
• Pipelines: Add checks in your CI/CD pipeline to validate the certificate chain for new deployments and prevent the use of untrusted certificates.
• Asset and patch process: Implement a sensible patch review cycle that fits the risk profile of your organisation. Regularly review security advisories from vendors and apply necessary updates.

7. Risks, Side Effects, and Roll Back

• Risk or side effect 2: Incorrectly configuring your web server could prevent legitimate connections. Back