How to remediate – Zimbra Collaboration Server Web Detection

1. Introduction

Zimbra Collaboration Server Web Detection indicates an open source messaging and collaboration application is running on a remote host. This matters because publicly accessible Zimbra instances can be targets for attackers seeking to gain access to sensitive email data and internal systems. Affected systems are typically mail servers or collaboration platforms used by businesses of all sizes. A successful attack could compromise confidentiality, integrity, and availability of email communications.

2. Technical Explanation

The vulnerability occurs because the web interface for Zimbra Collaboration Server has been detected. The detection plugin attempts to retrieve version information without credentials; however, if HTTP Basic authentication details are provided, it will attempt to retrieve the version from the SOAP API. This allows an attacker to potentially identify the installed Zimbra version and then search for known vulnerabilities.

• Root cause: The web interface is accessible and responds to requests revealing its presence.
• Exploit mechanism: An attacker can send HTTP requests to the Zimbra server to determine if it’s present, and potentially retrieve version information with valid credentials. This information can then be used to identify exploitable vulnerabilities.
• Scope: All systems running a publicly accessible Zimbra Collaboration Server instance are affected. Specific versions may have known vulnerabilities; see references for details.

3. Detection and Assessment

Confirming the presence of Zimbra is the first step in assessing vulnerability. A quick check can identify if the web interface is reachable, while a thorough method involves attempting to retrieve version information.

• Quick checks: Access the server’s web interface via a browser or using curl. If it displays a Zimbra login page, the service is present.
• Scanning: Nessus plugin ID 10384 can detect Zimbra Collaboration Server. Other vulnerability scanners may also have relevant plugins.
• Logs and evidence: Web server logs (e.g., Apache or Nginx) may show requests to paths associated with Zimbra, such as /zimbra/.

curl -I http://your-zimbra-server.com

4. Solution / Remediation Steps

The primary solution is to ensure the Zimbra server is running a supported version and has appropriate security measures in place.

4.1 Preparation

• No services need to be stopped for initial assessment, but stopping Zimbra is recommended during patching.
• Ensure you have access to the latest Zimbra patches and documentation. A roll back plan involves restoring from backup or snapshot.

4.2 Implementation

1. Step 1: Check the current Zimbra version using the methods described in section 3.
2. Step 2: Visit https://wiki.zimbra.com/wiki/Zimbra_Releases to determine if your version is supported and has any outstanding security patches.
3. Step 3: Download and install the latest available patch for your Zimbra version, following the official Zimbra documentation.

4.3 Config or Code Example

This vulnerability does not involve a specific configuration change; it requires updating the Zimbra software.

Before

N/A - Vulnerable Zimbra version

After

Updated to latest patched Zimbra version

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help mitigate this vulnerability.

• Practice 1: Patch cadence – Regularly update all software, including Zimbra, to address known vulnerabilities.
• Practice 2: Least privilege – Limit access to the Zimbra server and its data to only those users who require it.

4.5 Automation (Optional)

Automating patch deployment depends on your environment. Consider using configuration management tools.

# Example Ansible task - adapt for your environment
- name: Check Zimbra version
  command: /opt/zimbra/bin/zmversion
  register: zimbra_version
- name: Install Zimbra patch (example)
  apt:
    name: zimbra-patch-{{ zimbra_version.stdout }}
    state: latest
  when: zimbra_version.changed

5. Verification / Validation

Confirm the fix by verifying the updated Zimbra version and ensuring the web interface is no longer vulnerable.

• Post-fix check: Run curl -I http://your-zimbra-server.com and verify that the server header indicates the patched version.
• Re-test: Re-run the Nessus scan (plugin ID 10384) to confirm it no longer reports the vulnerability.
• Smoke test: Verify users can still log in to Zimbra and send/receive emails.
• Monitoring: Monitor web server logs for any unusual activity related to Zimbra.

curl -I http://your-zimbra-server.com

6. Preventive Measures and Monitoring

Proactive measures can prevent future occurrences.

• Baselines: Implement a security baseline that requires regular software updates, including Zimbra.
• Asset and patch process: Establish a regular patch review cycle for all systems, with documented approval processes.

7. Risks, Side Effects, and Roll Back

Patching can introduce risks; plan accordingly.

• Risk or side effect 1: Patch installation may cause temporary service downtime. Schedule patching during a maintenance window.
• Roll back: Restore from backup or snapshot taken prior to the patch installation.

8. References and Resources

Consult official Zimbra resources for further information.

• Vendor advisory or bulletin: https://www.zimbra.com/email-server-software
• NVD or CVE entry: No specific CVE is listed in the context provided.
• Product or platform documentation relevant to the fix: https://wiki.zimbra.com/wiki/Zimbra_Releases