Velocity: Fixing IP Limit Issues In Sonar

Experiencing issues with IP limits not functioning correctly in your Velocity setup with Sonar? You're not alone! This article dives deep into a reported bug where the IP limiting feature in Velocity, when used with Sonar, fails to prevent bot connections, despite other security measures like slow-attack protection working as expected. We'll explore the problem, the steps to reproduce it, and provide insights into potential solutions. Let’s get your server security back on track.

Understanding the Problem: IP Limit Not Working

The core issue reported is that the IP limiting feature within Velocity, a popular proxy server for Minecraft, does not effectively restrict connections based on IP addresses when used in conjunction with Sonar, a security plugin. This means that malicious actors can bypass the intended limitations and flood the server with bots, potentially leading to performance issues or even a denial-of-service (DoS) attack. While other security features, such as slow-attack protection, might function correctly, the failure of IP limiting leaves a significant vulnerability in the server's defenses. It’s crucial to address this problem because it directly impacts the server's stability and the gaming experience for legitimate players.

This vulnerability can be particularly concerning for server owners who rely on IP limits as a primary method for preventing abuse. Without effective IP limiting, the server becomes an easy target for botnets and other malicious activities. The report highlights a specific scenario where bots successfully bypassed the IP limit, even though the slow-attack protection was functioning as intended. This discrepancy suggests a potential conflict or misconfiguration between Velocity's IP limiting mechanism and Sonar's security protocols. It's important to investigate this interaction to identify the root cause and implement a reliable solution. Addressing this issue requires a thorough understanding of both Velocity's and Sonar's functionalities and how they interact with each other.

To effectively troubleshoot this problem, we need to consider various factors. First, it's crucial to confirm that the IP limit settings are correctly configured within Velocity. This involves checking the configuration files to ensure that the desired limits are set and that the feature is enabled. Second, we need to examine Sonar's configuration and logs to identify any potential conflicts or errors that might be interfering with Velocity's IP limiting functionality. This may involve adjusting Sonar's settings or updating the plugin to the latest version. Finally, it's essential to test the solution thoroughly to ensure that IP limits are functioning as expected and that bots are effectively blocked. This may require simulating bot attacks and monitoring the server's performance and security logs. By taking a systematic approach, we can effectively diagnose and resolve this issue, ensuring the server's security and stability.

Steps to Reproduce the Bug

To effectively address the bug, understanding how to reproduce it is crucial. Here are the steps outlined in the report to replicate the issue:

1. Install Velocity: Begin by setting up a Velocity proxy server. This is the foundation for replicating the bug, as it involves Velocity's IP limiting feature.
2. Install Sonar: Integrate the Sonar plugin with your Velocity setup. This step is essential as the issue seems to arise when these two are used together. Ensure both are correctly installed and configured according to their respective documentation.
3. Start Velocity with ONLY Sonar: Launch the Velocity server with only the Sonar plugin enabled. This isolates the interaction between Velocity's IP limiting and Sonar, helping to pinpoint the cause of the problem. It prevents other plugins from interfering with the test.
4. Simulate a DoS Attack: Use a tool like Soulfire to initiate a simulated Denial of Service (DoS) attack. This is a controlled way to test the server's resilience and observe how IP limiting behaves under stress. By mimicking a real attack, you can accurately assess the effectiveness of the security measures.
5. Observe Bot Connections: Monitor the server to see if bots are bypassing the IP limits. This is the key observation point. If bots successfully connect despite the IP limits being in place, it confirms the bug.

By following these steps, you can reliably reproduce the bug and gain a firsthand understanding of the issue. This will aid in the troubleshooting process and help you verify any potential solutions.

Analyzing the Sonar Dump

The Sonar dump provides valuable information about the server's environment and the configuration of Sonar itself. Let's break down the key sections and understand what they tell us:

• Memory: This section details the server's memory usage. The total memory is 1000 MiB, with a maximum of 7.8 GiB allocated. The free memory is 590.1 MiB, and the used memory is 409.9 MiB. This information can be useful for identifying potential memory-related issues, although in this case, the memory usage appears to be within reasonable limits. Monitoring memory usage is crucial for ensuring the server's stability and performance. High memory usage can indicate a memory leak or inefficient code, which can lead to crashes and slowdowns. By understanding the memory usage patterns, server administrators can optimize the server's configuration and identify potential problems before they escalate.
• Runtime: This section provides details about the Java Runtime Environment (JRE) being used. It shows that the server is running on OpenJDK 64-Bit Server VM, with JVM arguments including -Xms1000M and -Xmx8000M, which specify the initial and maximum heap sizes, respectively. The VM name is OpenJDK 64-Bit Server VM, the vendor is Debian, and the version is 17.0.17+10-Debian-1deb12u1. This information is important for ensuring compatibility and identifying potential JRE-related issues. Different JRE versions may have different performance characteristics and compatibility with plugins. By knowing the JRE version, administrators can ensure that the server is running on a stable and well-supported version.
• OS: This section provides information about the operating system. The server is running on Linux, with an amd64 architecture and version 6.1.0-30-amd64. Knowing the operating system and its version is crucial for troubleshooting compatibility issues and ensuring that the server is running on a supported platform. Different operating systems may have different performance characteristics and security vulnerabilities. By understanding the operating system environment, administrators can optimize the server's configuration and security settings.
• Sonar: This section details the Sonar plugin's information. The version is 2.1.41 (df049a70), the platform is VELOCITY, the Git branch is main, and the Git commit is df049a70. This information is essential for identifying the specific version of Sonar being used, which can be helpful for troubleshooting and identifying potential bugs or compatibility issues. Knowing the Sonar version allows administrators to check for known issues and updates, ensuring that the plugin is functioning correctly and that any security vulnerabilities are addressed. The Git branch and commit information can also be useful for tracking changes and identifying the specific code version being used.

In the context of the IP limit issue, the Sonar dump doesn't immediately reveal any glaring problems. However, it confirms the versions of Velocity and Sonar being used, which is a crucial first step in troubleshooting. It also indicates that the server has sufficient memory allocated, ruling out memory constraints as a primary cause. The next step is to analyze the server logs and configuration files in more detail to identify potential conflicts or misconfigurations.

Examining Endpoint Server Logs

The provided logs from the endpoint server offer a glimpse into the connections being made. We can see several bots (Bot_1, Bot_8, Bot_17, Bot_3) connecting from the same IP address (127.0.0.1), which is the localhost. This immediately suggests that the IP limiting is not functioning as expected, as multiple connections from the same IP address should be restricted if the IP limit is in place. The logs also show that these bots are being teleported to the same location, which is a common behavior for bot attacks.

The logs also contain information about player UUIDs, login times, and disconnections. While these details are helpful for general server monitoring, they don't directly explain the IP limiting issue. However, the repeated login attempts from the same IP address, followed by disconnections, further reinforce the observation that bots are bypassing the IP limits.

To further investigate this issue, we need to examine the Velocity configuration files and Sonar settings. It's possible that there's a misconfiguration that's preventing the IP limits from being enforced. For example, the IP limit might be set too high, or there might be an exception in the configuration that's allowing connections from localhost. Additionally, it's important to check for any conflicting settings between Velocity and Sonar that might be interfering with the IP limiting functionality.

Potential Solutions and Workarounds

Given the information gathered, here are some potential solutions and workarounds to address the IP limit issue:

1. Review Velocity Configuration: Carefully examine the Velocity configuration file (velocity.toml) to ensure that the IP limit settings are correctly configured. Look for parameters related to connection limits, such as player-per-ip-limit, and verify that they are set to the desired values. Make sure that the IP limiting feature is enabled and that there are no exceptions or whitelists that might be allowing bot connections.
2. Check Sonar Settings: Investigate Sonar's configuration to identify any settings that might be interfering with Velocity's IP limiting functionality. Look for options related to connection management, security protocols, and IP filtering. It's possible that Sonar has its own IP limiting mechanism that's conflicting with Velocity's, or that there's a setting that's inadvertently disabling Velocity's IP limits.
3. Update Velocity and Sonar: Ensure that you are running the latest versions of both Velocity and Sonar. Software updates often include bug fixes and performance improvements that can address known issues. Check the official websites or repositories for updates and follow the instructions for upgrading. Outdated software can have vulnerabilities and bugs that are not present in newer versions. Keeping the software up to date is crucial for ensuring security and stability.
4. Investigate Plugin Conflicts: If you have other plugins installed on your server, there's a possibility that one of them is conflicting with Velocity or Sonar. Try disabling plugins one by one to see if the IP limiting starts working correctly. If you identify a conflicting plugin, you can either remove it or try to configure it to work harmoniously with Velocity and Sonar.
5. Implement a Firewall: As a temporary workaround, consider implementing a firewall to restrict connections from specific IP addresses. This can help to mitigate the impact of bot attacks while you troubleshoot the underlying issue with Velocity and Sonar. Firewalls provide an additional layer of security and can be configured to block malicious traffic based on various criteria, such as IP address, port, and protocol.
6. Contact Velocity and Sonar Support: If you've tried the above solutions and are still experiencing issues, reach out to the support teams for Velocity and Sonar. They may be able to provide specific guidance or identify a bug in their software. When contacting support, provide detailed information about your setup, including the versions of Velocity and Sonar, your configuration files, and the steps you've taken to reproduce the issue.

Conclusion

Troubleshooting IP limit issues in Velocity, especially when using plugins like Sonar, requires a systematic approach. By understanding the problem, reproducing the bug, analyzing logs, and exploring potential solutions, you can effectively address the vulnerability and protect your server from bot attacks. Remember to review configurations, update software, and consider temporary workarounds like firewalls. If all else fails, don't hesitate to seek support from the Velocity and Sonar communities.

For more information on Minecraft server security, you might find resources on reputable websites like OWASP helpful. They offer extensive guides and best practices for securing web applications and servers.