1. Introduction
The vulnerability “Apache Struts 2 Config Browser Detected” refers to the presence of the Apache Struts 2 Config Browser Plugin on a web application. This plugin is designed for runtime viewing of Struts configuration, but its existence can expose sensitive information about the application’s structure and versioning, potentially aiding attackers in identifying vulnerabilities. Web applications using Apache Struts 2 are typically affected. A successful exploit could lead to information disclosure, impacting confidentiality.
2. Technical Explanation
The Apache Struts 2 Config Browser Plugin provides a web interface for viewing the application’s configuration details. This includes version numbers, loaded configurations and accessible action URLs. An attacker can access this information remotely without authentication if the plugin is publicly available. The primary risk is information disclosure that could be used to target known vulnerabilities in specific versions of Struts or identify attack vectors.
- Root cause: Presence of a debugging/development module (Config Browser Plugin) in a production environment.
- Exploit mechanism: An attacker simply accesses the plugin’s URL, which reveals configuration details. No complex exploit is required for initial information gathering.
- Scope: Web applications running Apache Struts 2 with the Config Browser Plugin installed.
3. Detection and Assessment
To confirm vulnerability, first check if the plugin’s URL is accessible. A thorough method involves scanning the application for the presence of specific files associated with the plugin.
- Quick checks: Attempt to access URLs like
/config-browseror/struts2-config-browserin a web browser. - Scanning: Nessus and other vulnerability scanners may have signatures for detecting the Apache Struts 2 Config Browser Plugin.
- Logs and evidence: Web server logs might show access attempts to the plugin’s URL.
curl -I http://your-application/config-browser4. Solution / Remediation Steps
To fix this issue, remove the Apache Struts 2 Config Browser Plugin or restrict access to it. Only include steps that apply to this vulnerability.
4.1 Preparation
- Ensure you have a rollback plan in case of issues, such as restoring from backup. A change window may be required depending on your environment.
4.2 Implementation
- Step 1: Locate the Config Browser Plugin directory within your Struts application’s webapp folder (usually under WEB-INF/lib).
- Step 2: Delete the plugin’s JAR file from the webapp folder.
- Step 3: Restart the web application service to apply the changes.
4.3 Config or Code Example
Before
After
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: Secure Configuration – Avoid deploying debugging or development modules in production environments.
- Practice 2: Least Privilege – Restrict access to sensitive application components and configuration files.
4.5 Automation (Optional)
# Example Bash Script to remove plugin from webapp directory
# WARNING: Ensure correct path before running!
rm -f /path/to/webapp/WEB-INF/lib/struts2-config-browser.jar
5. Verification / Validation
Confirm the fix by verifying that the plugin’s URL is no longer accessible and that it has been removed from the application’s classpath. Include a simple service smoke test.
- Post-fix check: Attempt to access
http://your-application/config-browser; expect a 404 or other error indicating the resource is not found. - Re-test: Re-run the curl command from section 3 and confirm it returns an error code (e.g., 404).
- Monitoring: Monitor web server logs for any unexpected errors related to missing configuration files.
curl -I http://your-application/config-browser6. 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 security baselines to exclude debugging modules from production deployments.
- Pipelines: Implement static analysis checks in CI/CD pipelines to detect and prevent deployment of development-related files.
- Asset and patch process: Regularly review application dependencies and configurations for unnecessary components.
7. Risks, Side Effects, and Roll Back
- Risk or side effect 1: Removing the plugin may impact developers who rely on it for debugging purposes.
- Risk or side effect 2: In rare cases, removing a file could cause unexpected application errors if other components depend on it (unlikely).
- Roll back: Restore the plugin’s JAR file to the webapp folder and restart the web application service.
8. References and Resources
- Vendor advisory or bulletin: https://cwiki.apache.org/confluence/display/WW/S2-043
- NVD or CVE entry: Not applicable for this specific detection, but related vulnerabilities may be listed on the NVD website.
- Product or platform documentation relevant to the fix: https://struts.apache.org/plugins/config-browser/