Web application firewalls (WAFs) are essential for protecting your apps from common threats like SQL injection, XSS, and bot attacks. Whether you're deploying a side project or securing production APIs, a good WAF can block many threats before they even reach your backend.
And the best part? You donโt need to pay to get solid protection.
Here are 5 of the most reliable, developer-friendly open-source WAFs available in 2025.
๐ก๏ธ 1. SafeLine WAF
SafeLine is a high-performance reverse proxy with a built-in, intelligent Web Application Firewall. It protects against SQL injection, XSS, and HTTP Flood using advanced semantic analysis โ making it a solid pick for developers who want strong, modern protection out of the box.
It features a user-friendly interface, detailed traffic analytics, and supports flexible deployment across Nginx, Docker, Kubernetes, and more. As an open-source project with over 16.4K stars on GitHub, itโs quickly becoming a popular choice in the devsecops world.
๐ 2. ModSecurity
ModSecurity is one of the most established open-source WAFs and integrates with Apache, Nginx, and IIS. It uses the OWASP Core Rule Set (CRS) and is highly configurable.
However, its flexibility comes at a cost โ expect a steeper learning curve and potentially more tuning to avoid false positives.
โ๏ธ 3. NAXSI
Short for "Nginx Anti XSS & SQL Injection," NAXSI is a minimalist WAF tailored specifically for Nginx. It relies on a whitelist-based model and rule scoring system. Setup requires manual tuning, but once configured, itโs lightweight and effective for common attack types.
๐ 4. OpenResty + Lua WAF
If you prefer building custom WAF logic yourself, OpenResty gives you full control through Lua scripting. This stack is not beginner-friendly, but for advanced use cases โ like behavior-based detection or deep integration with business logic โ it can be very powerful.
Several Lua-based WAF frameworks (e.g., lua-resty-waf) can help you get started.
๐งฐ 5. AWS WAF (Free Tier)
While not open-source, AWS WAF offers a generous free tier and integrates tightly with CloudFront and ALB. You can use prebuilt rule groups or define custom ones through AWS WAFโs UI or API. Itโs convenient for teams already using the AWS stack but comes with vendor lock-in.
โจ Final Thoughts
Choosing a WAF depends on your tech stack, performance needs, and how much tuning you're willing to do.
- If you want full control: go with ModSecurity or OpenResty
- If you prefer something lean and focused: NAXSI is a good fit
- If youโre looking for a modern, Go-based WAF with easy deployment: give SafeLine a try
- For AWS users: AWS WAF is a practical option
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