How to remediate – Apache Solr Detection

1. Introduction

The remote web server hosts Apache Solr, an open source search platform. This software is used for indexing and searching large volumes of data. A publicly accessible instance could allow attackers to gather information about the system and potentially identify further attack vectors. Confidentiality, integrity, and availability may be impacted if exploited.

2. Technical Explanation

Apache Solr is a Java-based search platform that provides an administrative interface for managing its configuration and functionality. This interface can be accessed remotely without authentication by default. An attacker could access this interface to enumerate system details, potentially leading to further exploitation. There is no known CVE associated with this specific detection, but it represents a high risk due to the potential exposure of sensitive information. For example, an attacker could identify installed plugins and their versions, which might reveal vulnerabilities in those components.

• Root cause: Default configuration allows remote access without authentication.
• Exploit mechanism: An attacker sends HTTP requests to the Solr administrative interface to gather system information.
• Scope: Apache Solr installations accessible from the internet or untrusted networks.

3. Detection and Assessment

Confirming whether a system is vulnerable involves checking for an open Solr instance and verifying if it allows unauthenticated access.

• Quick checks: Use curl to check the response from the Solr admin interface. A successful response indicates the service is running.
• Scanning: Nessus plugin ID 16823 can identify open Apache Solr instances. This is an example only, and other scanners may provide similar functionality.
• Logs and evidence: Check web server logs for requests to paths associated with Solr (e.g., /solr/admin/).

curl http://target_ip:8983/solr/admin/info.json

4. Solution / Remediation Steps

Secure the Apache Solr instance by restricting access or implementing authentication.

4.1 Preparation

• Ensure you have access to the Solr configuration files and understand how to restart the service. Roll back plan: Restore from snapshot or revert configuration changes.
• A change window may be needed depending on production impact. Approval should be sought from system owners.

4.2 Implementation

1. Step 1: Configure Solr to bind only to localhost (127.0.0.1). This prevents external access.
2. Step 2: Implement authentication for the Solr admin interface using a strong username and password.
3. Step 3: Restart the Solr service to apply the changes.

4.3 Config or Code Example

Before

# solr.xml - default configuration
<listenAddress>0.0.0.0:8983</listenAddress>

After

# solr.xml - secure configuration
<listenAddress>127.0.0.1:8983</listenAddress>

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: Least privilege to reduce the impact if exploited by limiting access to only necessary users and systems.
• Practice 2: Secure defaults to ensure that services are configured with the most secure settings out-of-the-box.

4.5 Automation (Optional)

# Example Ansible task to modify solr.xml
- name: Secure Solr listen address
  lineinfile:
    path: /opt/solr/server/solr.xml
    regexp: '<listenAddress>0.0.0.0:8983</listenAddress>'
    line: '<listenAddress>127.0.0.1:8983</listenAddress>'
  notify: Restart Solr

5. Verification / Validation

Confirm the fix by verifying that external access to the Solr admin interface is blocked and authentication is required.

• Post-fix check: Use curl from a remote system. A connection timeout or error message indicates successful restriction of access.
• Re-test: Re-run the initial curl command from a remote system to confirm that unauthenticated access is no longer possible.
• Monitoring: Monitor web server logs for failed login attempts or unauthorized access attempts to the Solr admin interface. This is an example only, and specific log patterns may vary.

curl http://target_ip:8983/solr/admin/info.json - Connection timed out

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 a security baseline or policy to include requirements for secure Solr configuration (e.g., restricting access and enabling authentication).
• Pipelines: Add checks in CI/CD pipelines to scan for open ports and insecure configurations during deployment.
• Asset and patch process: Implement a regular review cycle for Solr configurations to ensure they remain secure.

7. Risks, Side Effects, and Roll Back

• Roll back: Restore the original solr.xml file and restart the service.

8. References and Resources

• Vendor advisory or bulletin: http://lucene.apache.org/solr/
• NVD or CVE entry: Not applicable for this specific detection.
• Product or platform documentation relevant to the fix: https://solr.apache.org/guide/security/index.html