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SafeLine WAF: Open Source Web Application Firewall with Zero-Day Detection and Bot Protection. From zero-day exploits to large-scale bot attacks — the demand for a powerful, self-hosted, and user-friendly web application security solution has never been greater. SafeLine is currently the most starred open-source Web Application Firewall (WAF) on GitHub, with over 16.4K stars and a rapidly growing global user base. This walkthrough covers what SafeLine is, how it works, and why it's becoming the go-to solution over cloud-based WAFs. What is SafeLine WAF? SafeLine is a self-hosted web application firewall that acts as a reverse proxy, filtering and monitoring HTTP/HTTPS traffic to block malicious requests before they reach your backend web applications. Unlike cloud-based WAFs, SafeLine runs entirely on your own servers—giving you unmatched visibility and data sovereignty. Key Features of SafeLine WAF Comprehensive Attack Prevention SafeLine effectively blocks a wide range of common and advanced web attacks, including SQL injection(SQLi), cross-site scripting (XSS), OS command injection, CRLF injection, XML External Entity (XXE) attacks, Server Side Request Forgery (SSRF), and directory traversal, etc. Zero-Day Detection via Semantic Analysis Unlike traditional signature-based WAFs, SafeLine uses a patented semantic analysis engine that deeply parses HTTP traffic semantics. This approach enables it to detect complex and zero-day attacks with high accuracy, resulting in an industry-leading detection rate of 99.45% and an ultra-low false positive rate of 0.07%. (The chart below compares SafeLine with the two versions of a globally recognized open-source WAF.) Robust Bot Protection SafeLine delivers comprehensive, multi-layered defenses against automated bot attacks, a growing threat vector responsible for credential stuffing, malicious scraping, inventory hoarding, and vulnerability scanning. It combines several out-of-box powerful mechanisms: HTTP Flood DDoS Mitigation HTTP flood DDoS attacks attempt to overwhelm servers by sending massive volumes of HTTP requests in a short period of time. These attacks can exhaust server resources, degrade performance, or take applications offline entirely. To counter this, SafeLine implements rate limiting to cap request frequency and mitigate abuse. These measures are highly configurable, allowing defenders to tailor thresholds based on real-world traffic patterns. For sudden traffic spikes—whether legitimate or malicious—SafeLine provides a virtual waiting room mechanism. This ensures service availability by queuing excess users and releasing them gradually, preventing backend overload while maintaining a fair and orderly access experience. Authentication Challenges SafeLine is also designed with Zero Trust principles in mind—never trust, always verify. It offers configurable visitor authentication to secure access to protected applications, enhancing security through enforced identity checks. As a built-in identity gateway, it supports modern authentication protocols such as OIDC and integrates seamlessly with identity providers like GitHub and others. SafeLine also supports Single Sign-On (SSO) to streamline user authentication and simplify login experience in the meantime. Best of all, these enterprise-grade identity features are included for free. Simple Deployment in Minutes SafeLine is designed for quick setup and easy management. It requires the following environment to be installed and run: Once the environment is ready, installation takes just a few minutes with a single command. A user-friendly, wizard-based interface guides you through configuration. Full documentation is available here. Why Choose SafeLine Over Cloud-Based WAFs? Unlike traditional cloud-based WAFs that route your traffic through third-party infrastructure, SafeLine offers complete deployment autonomy. Here are the advantages: Get SafeLine — free forever for personal use, with optional 7-day Pro trial. Use Cases Ideal for SafeLine SafeLine is a versatile solution built for a wide range of web application security needs. It's particularly well-suited for: Final Words SafeLine stands out as a powerful, open-source alternative to traditional cloud-based WAFs. With cutting-edge zero-day detection, robust bot mitigation, and zero trust–aligned identity features—all bundled into a self-hosted, easy-to-deploy package—SafeLine empowers developers, security teams, and organizations of all sizes to take control of their web security. Get SafeLine — free forever for personal use, with optional 7-day Pro trial.