When it comes to protecting your web applications, a reliable Web Application Firewall (WAF) is non-negotiable. Two popular open source WAFs—SafeLine and ModSecurity—offer very different approaches to application-layer security.
In this post, we’ll walk through their core differences, real-world usage, and what kind of developers or teams they’re best suited for.
What Is ModSecurity?
ModSecurity is one of the earliest open source WAFs. Originally built as an Apache module, it now supports Nginx and IIS as well. It's best known for its rule-based detection system, using the OWASP Core Rule Set (CRS) to catch common vulnerabilities like SQLi and XSS.
It’s flexible, customizable, and widely used—but it can also be complex to configure, heavy on false positives, and lacks modern detection capabilities out of the box.
What Is SafeLine?
SafeLine is a newer open source WAF developed by Chaitin Tech. It takes a different approach to detection: instead of relying on traditional rules, it leverages an intelligent semantic analysis engine. This allows SafeLine to detect complex attacks that bypass regex-based rules.
It runs as a reverse proxy based on Nginx, supports Docker and Kubernetes deployment, and is production-ready out of the box—no license, no hidden features.
Feature Comparison
| Feature | ModSecurity | SafeLine |
|---|---|---|
| Detection Model | Rule-based (regex + CRS) | Intelligent semantic analysis engine |
| Default Ruleset | OWASP CRS | Built-in intelligent engine |
| False Positive Rate | Moderate to high | Low (context-aware detection) |
| Performance | Medium | High (optimized Nginx-based) |
| Learning Curve | Steep (manual tuning needed) | Beginner-friendly (auto-detection works) |
| Custom Rules | Manual rule writing required | Supports extensions but works out of box |
| Logging & Visibility | Basic logs | Rich attack logs + dashboard UI |
| Reverse Proxy Mode | Yes | Yes |
| Transparent Proxy Mode | Partial (complex setup) | Yes |
| Docker/K8s Support | Yes (manual setup) | Yes (ready-made images) |
| Maintenance & Community | Mature but slower development | Actively maintained |
When to Use ModSecurity
- You’re in a regulated environment where OWASP CRS is a requirement.
- You need fine-grained control and have security engineers on your team.
- You’re already running Apache or legacy WAF systems.
When to Use SafeLine
- You want a plug-and-play WAF with low false positives.
- You’re running modern stacks (Nginx, Docker, Kubernetes).
- You need semantic-level detection that catches obfuscated attacks.
- You prefer active maintenance and a cleaner user experience.
Final Thoughts
ModSecurity has been the go-to open source WAF for over a decade, but it shows its age in many areas. SafeLine brings a fresh take on detection, built for modern web stacks and cloud-native deployments.
If you're tired of false positives, brittle regex rules, or just want to try a more intelligent WAF, SafeLine is worth exploring.
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