How to remediate – XMPP Cleartext Authentication

1. Introduction

The XMPP Cleartext Authentication vulnerability means a service is allowing usernames and passwords to be sent without encryption. This poses a risk as attackers can intercept credentials during transmission, potentially gaining unauthorised access to accounts. Systems running XMPP servers, like those used for instant messaging or presence information, are usually affected. A successful exploit could compromise the confidentiality of user logins.

2. Technical Explanation

The vulnerability occurs when an XMPP server supports authentication methods that do not encrypt credentials. An attacker can use a network sniffer to capture usernames and passwords as they are sent in plain text. This is typically possible because the connection isn’t secured with TLS/SSL, or a weaker, insecure authentication method is enabled alongside stronger ones.

• Root cause: The XMPP server allows unencrypted authentication mechanisms like PLAIN, CRAM-MD5, or DIGEST-MD5 to be used.
• Exploit mechanism: An attacker intercepts network traffic between the client and server using tools such as Wireshark. They then extract the cleartext credentials from the captured packets. For example, an attacker on the same network could capture a PLAIN authentication exchange.
• Scope: XMPP servers running various software packages are affected, including ejabberd, Openfire, and Prosody. Specific versions depend on whether default configurations have been changed or if vulnerable authentication methods have been explicitly enabled.

3. Detection and Assessment

You can confirm a system is vulnerable by checking the server’s configuration for supported authentication mechanisms and by attempting to connect using an insecure method.

• Quick checks: Use `xmppping` to list supported auth methods: xmppping -c yourserver.com. Look for PLAIN, CRAM-MD5 or DIGEST-MD5 in the output.
• Scanning: Nessus plugin ID 16394 can detect cleartext authentication on XMPP servers. This is an example only; results may vary depending on scanner configuration.
• Logs and evidence: Check server logs for successful authentications using PLAIN, CRAM-MD5 or DIGEST-MD5. Log locations depend on the specific XMPP server software used.

xmppping -c yourserver.com

4. Solution / Remediation Steps

Disable cleartext authentication mechanisms in the XMPX configuration to prevent attackers from intercepting credentials.

4.1 Preparation

• A change window may be required depending on business impact; approval from a system owner might be needed.

4.2 Implementation

1. Step 1: Edit the XMPX server’s configuration file (e.g., `xmppd.conf` for ejabberd).
2. Step 2: Comment out or remove any lines that enable PLAIN, CRAM-MD5, or DIGEST-MD5 authentication.
3. Step 3: Ensure TLS/SSL is enabled and properly configured for all XMPX connections.
4. Step 4: Restart the XMPX server to apply the changes.

4.3 Config or Code Example

Before

# Authentication methods
auth_methods: [PLAIN, CRAM-MD5, DIGEST-MD5, TLS]

After

# Authentication methods
auth_methods: [TLS]

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this issue and similar vulnerabilities.

• Practice 1: Least privilege – limit the impact of compromised credentials by granting only necessary access rights.
• Practice 2: Secure defaults – configure services with strong security settings out-of-the-box, disabling insecure options like cleartext authentication.

4.5 Automation (Optional)

If using a configuration management tool, you can automate the removal of insecure authentication methods.

# Example Ansible task to remove insecure auth methods from ejabberd config
- name: Remove insecure authentication methods
  lineinfile:
    path: /etc/ejabberd/xmppd.conf
    regexp: '^auth_methods: [PLAIN, CRAM-MD5, DIGEST-MD5'
    line: '# Authentication methods'
    state: absent

5. Verification / Validation

Confirm the fix by checking that insecure authentication methods are no longer supported and attempting a connection using an insecure method should fail.

• Post-fix check: Run `xmppping -c yourserver.com` again; TLS should be the only listed auth method.
• Re-test: Re-run the earlier detection to show that PLAIN, CRAM-MD5 and DIGEST-MD5 are no longer supported.
• Smoke test: Verify users can still log in using TLS/SSL authentication.
• Monitoring: Monitor server logs for failed authentication attempts using PLAIN, CRAM-MD5 or DIGEST-MD5 as an example alert.

xmppping -c yourserver.com

6. Preventive Measures and Monitoring

Regular security baselines and pipeline checks can help prevent this issue from recurring.

• Baselines: Update a security baseline or policy to require TLS/SSL for all XMPX connections, including disabling insecure authentication methods.
• Pipelines: Add static analysis (SAST) checks in your CI/CD pipeline to identify and block configurations with cleartext authentication enabled.
• Asset and patch process: Implement a regular review cycle of server configurations to ensure they adhere to security best practices.

7. Risks, Side Effects, and Roll Back

Disabling insecure authentication methods could temporarily disrupt users who rely on them (though this is unlikely).

• Risk or side effect 1: Users using older clients that only support cleartext authentication may be unable to connect.
• Roll back: Restore the original XMPX server configuration file and restart the service.

8. References and Resources

Links to official advisories and documentation related to this vulnerability.

• Vendor advisory or bulletin: [https://support.ejabberd.com/knowledge-base/security-hardening-guide/](https://support.ejabberd.com/knowledge-base/security-hardening-guide/)
• NVD or CVE entry: No specific CVE is associated with this general vulnerability, but search for XMPP vulnerabilities on the NVD website ([https://nvd.nist.gov/](https://nvd.nist.gov/)).
• Product or platform documentation relevant to the fix: Refer to your XMPX server’s official documentation for configuration details.