How to remediate – XMPP Service STARTTLS Command Support

1. Introduction

The XMPP Service STARTTLS Command Support vulnerability means that an instant messaging service allows traffic encryption using the STARTTLS command. This is a common feature, but it needs careful management to ensure security isn’t weakened. Systems typically affected are those running XMPP servers like ejabberd, Openfire or similar platforms used for internal and external communication. A successful attack could lead to eavesdropping on sensitive communications, impacting confidentiality.

2. Technical Explanation

• Exploit mechanism: An attacker can intercept the connection and attempt to downgrade the encryption protocol or exploit weaknesses in the TLS configuration. For example, they might use a tool like Wireshark to observe the STARTTLS handshake and manipulate it.
• Scope: XMPP servers running any version that supports STARTTLS are potentially affected. Specific configurations with weak ciphers or missing certificate validation are more vulnerable.

3. Detection and Assessment

Confirming vulnerability involves checking if the service advertises STARTTLS support. A thorough assessment requires examining the TLS configuration.

• Quick checks: Use telnet to connect to the XMPP server on port 5222 (default) and send the ‘STARTTLS’ command. If the server responds with a positive indication, it supports STARTTLS.

  telnet your_xmpp_server 5222
  Trying ...
  Connected to your_xmpp_server.
  STARTTLS
  +OK Using TLS

• Scanning: Nessus plugin ID 16478 (XMPP STARTTLS Support) can identify servers supporting STARTTLS. This is an example only and may require updating.
• Logs and evidence: Examine XMPP server logs for successful STARTTLS negotiations. The exact log format varies by server, but look for messages indicating TLS handshake completion.

4. Solution / Remediation Steps

The solution focuses on ensuring strong TLS configuration when using STARTTLS.

4.1 Preparation

• Changes may require a scheduled maintenance window, depending on your environment and impact tolerance. Approval from the IT security team is recommended.

4.2 Implementation

1. Step 1: Review the XMPP server’s TLS configuration to ensure strong ciphers are enabled (e.g., AES-256-GCM).
2. Step 2: Disable weak or outdated ciphers that may be vulnerable to attacks.
3. Step 3: Ensure proper certificate validation is configured, including checking the certificate chain and revocation status.
4. Step 4: Restart the XMPP service to apply the changes.

4.3 Config or Code Example

Before

# Example ejabberd config snippet (insecure)
{ssl, [{version, 'TLSv1'}]}

After

# Example ejabberd config snippet (secure)
{ssl, [{version, 'TLSv1_2'}, {version, 'TLSv1_3'}, {ciphers, ["AES256-GCM-SHA384"]}]}

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.

• Practice 1: Least privilege – limit access to the XMPP server configuration to authorized personnel only, reducing the risk of malicious changes.
• Practice 2: Secure defaults – configure the XMPP server with strong TLS settings by default, minimizing the need for manual intervention.
• Practice 3: Patch cadence – Regularly update the XMPP server software to address known vulnerabilities in the TLS implementation.

4.5 Automation (Optional)

If suitable, provide a small script or infrastructure code that applies the fix at scale.

# Example Ansible task to update ejabberd config
- name: Update ejabberd TLS configuration
  lineinfile:
    path: /etc/ejabberd/ejabberd.yml
    regexp: '^ {ssl, ' 
    line: '{ssl, [{version, 'TLSv1_2'}, {version, 'TLSv1_3'}, {ciphers, ["AES256-GCM-SHA384"]}]}'

5. Verification / Validation

Confirm the fix by verifying the updated TLS configuration and ensuring STARTTLS negotiation uses strong ciphers.

• Post-fix check: Use telnet to connect to the XMPP server and send ‘STARTTLS’. Check the server’s response for supported ciphers. The output should show AES256-GCM-SHA384 or similar secure ciphers.

  telnet your_xmpp_server 5222
  Trying ...
  Connected to your_xmpp_server.
  STARTTLS
  +OK Using TLS
  (Check the negotiated cipher suite in Wireshark or similar)

• Re-test: Re-run the telnet command from step 3. Detection tools should no longer flag weak ciphers.
• Monitoring: Monitor XMPP server logs for TLS handshake errors or attempts to use unsupported ciphers.

6. Preventive Measures and Monitoring

Suggest only measures that are relevant to the vulnerability type.

• Baselines: Update your security baseline to require strong TLS configurations for all XMPP servers. For example, CIS benchmarks provide guidance on secure settings.
• Asset and patch process: Implement a regular patch review cycle for the XMPP server software to address known TLS vulnerabilities promptly.

7. Risks, Side Effects, and Roll Back

List known risks or service impacts from the change.

• Risk or side effect 1: Disabling weak ciphers may cause compatibility issues with older clients that do not support strong encryption. Mitigation involves identifying and upgrading those clients.
• Roll back: Restore the original XMPX server configuration file. Restart the service. Verify connectivity.

8. References and Resources

Link only to sources that match this exact vulnerability.

• Vendor advisory or bulletin: Check your specific XMPP vendor’s documentation for TLS configuration guidance.
• NVD or CVE entry: While there isn’t a direct CVE for STARTTLS support, search NVD for vulnerabilities related to your XMPX