1. Introduction
Apache Flink Web UI Detection identifies instances of the Apache Flink web user interface running on a remote host. Apache Flink is an open-source framework for stream and batch processing. This detection helps identify potential exposure points within your infrastructure, as the web UI can be a target for attackers. A successful exploit could lead to information disclosure or potentially remote code execution.
2. Technical Explanation
The vulnerability lies in the presence of the Apache Flink Web UI, which is accessible by default on port 8081. An attacker can access this interface to gather information about the running cluster and its configuration. While not a direct exploit, it represents an attack surface that should be secured or removed if unnecessary. There are no known CVEs associated with simply *detecting* the UI; however, vulnerabilities in Flink itself could be exploited via the web interface.
- Root cause: The Apache Flink Web UI is exposed and accessible without authentication by default.
- Exploit mechanism: An attacker can access the web UI through a browser to gather information about the cluster, potentially leading to further exploitation of vulnerabilities within Flink itself.
- Scope: Affected systems are those running Apache Flink with the web interface enabled.
3. Detection and Assessment
You can confirm the presence of the Flink Web UI by checking for open port 8081 or accessing the UI in a browser. Scanning tools may also identify it based on HTTP headers.
- Quick checks: Use `netstat -tulnp | grep 8081` to check if port 8081 is listening.
- Scanning: Nessus plugin ID 16739 or OpenVAS script http_apache-flink can identify the UI, but results may vary.
- Logs and evidence: Web server logs (if a reverse proxy is used) might show access attempts to the Flink web UI endpoint.
netstat -tulnp | grep 80814. Solution / Remediation Steps
The primary solution is to secure or disable the Apache Flink Web UI if it’s not required. If needed, implement authentication and authorization mechanisms.
4.1 Preparation
- Ensure you have access to restart the Flink services. A roll back plan involves restoring from the snapshot or restarting the service with the original configuration.
- A change window may be required depending on your environment and production impact.
4.2 Implementation
- Step 1: Edit the `flink-conf.yaml` file to disable the web UI by setting `rest.flume-monitoring.enabled: false`.
- Step 2: Restart the Flink job manager service for the changes to take effect.
4.3 Config or Code Example
Before
rest:
flume-monitoring:
enabled: true
After
rest:
flume-monitoring:
enabled: false
4.4 Security Practices Relevant to This Vulnerability
Least privilege and secure defaults are relevant practices here. Limiting network access reduces the attack surface, while disabling unnecessary services minimizes potential exposure points.
- Practice 1: Least privilege – only allow necessary users or systems access to the Flink cluster.
- Practice 2: Secure Defaults – Disable unused features like the web UI by default.
4.5 Automation (Optional)
If using configuration management tools, you can automate the modification of `flink-conf.yaml`.
# Example Ansible task
- name: Disable Flink Web UI
lineinfile:
path: /opt/flink/conf/flink-conf.yaml
regexp: 'rest.flume-monitoring.enabled:'
line: 'rest.flume-monitoring.enabled: false'
notify: Restart Flink Job Manager
5. Verification / Validation
Confirm the fix by checking that port 8081 is no longer accessible or that authentication is required to access the web UI.
- Post-fix check: Run `netstat -tulnp | grep 8081` and verify that nothing is listening on port 8081.
- Re-test: Re-run the initial detection method (accessing the web UI) to confirm it’s no longer accessible without authentication.
- Monitoring: Monitor system logs for errors related to the Flink job manager or web UI.
netstat -tulnp | grep 80816. Preventive Measures and Monitoring
Regular security baselines and vulnerability scanning can help identify exposed services like the Flink Web UI. Implement a patch management process to address vulnerabilities in Apache Flink itself. For example, update your CIS benchmark or GPO/Intune settings.
7. Risks, Side Effects, and Roll Back
- Risk or side effect 1: Loss of visual monitoring through the web UI. Mitigation: Implement alternative monitoring tools.
- Roll back: Restore the original `flink-conf.yaml` file and restart the Flink job manager service.
8. References and Resources
- Vendor advisory or bulletin: Apache Flink Security Documentation
- NVD or CVE entry: Not applicable for detection only.
- Product or platform documentation relevant to the fix: Flink REST Configuration