Overview
ModSecurity is the grandfather of web application firewalls and remains the most widely deployed WAF in the world. As an open source project, it provides the core WAF engine that powers many commercial solutions and protects millions of websites through integration with Apache, Nginx, and IIS web servers.
Originally developed by Ivan Ristic at Thinking Stone, ModSecurity has been maintained by Trustwave and is now a community-driven project. Version 3.0 introduced a standalone library (libmodsecurity) that can be integrated with any platform, expanding its reach beyond traditional web servers.
ModSecurity's power lies in its flexibility. Combined with the OWASP Core Rule Set (CRS), it provides comprehensive protection against common web attacks. For organizations with security expertise, ModSecurity offers unmatched customization possibilities - every aspect of request inspection and response can be tailored.
Ratings Breakdown
Key Features
OWASP Core Rule Set
Comprehensive, community-maintained rule set providing protection against OWASP Top 10 and more.
Custom Rules
Powerful SecRule language for creating custom detection logic based on any request/response attribute.
Real-Time Request Analysis
Inspect and analyze every HTTP transaction with access to full request and response data.
Audit Logging
Detailed logging of security events for forensics, compliance, and monitoring.
Virtual Patching
Create temporary rules to protect against vulnerabilities while permanent fixes are developed.
Data Loss Prevention
Inspect response bodies to prevent sensitive data leakage.
Pros & Cons
Pros
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Completely free
No licensing costs ever. Only pay for the infrastructure and expertise to run it.
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Maximum flexibility
Every aspect can be customized. If you can think it, you can probably implement it.
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No vendor lock-in
Open source with multiple deployment options. Your rules work anywhere ModSecurity runs.
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Extensive community
Large community, extensive documentation, and the OWASP CRS provides excellent baseline protection.
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Proven technology
Battle-tested across millions of sites over 20+ years. Known vulnerabilities and limitations are well-documented.
Cons
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Requires expertise to operate
No managed service option. You need staff who understand WAF concepts and rule writing.
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Performance overhead
Running on your own servers consumes resources. Complex rule sets can add latency.
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High false positive rate out of box
OWASP CRS requires tuning for each application to reduce false positives.
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No built-in management UI
Configuration is file-based. Third-party or custom UIs needed for easier management.
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Self-managed updates
You're responsible for updating ModSecurity and rule sets. No automatic protection against new threats.
Pricing
Pricing model: Free (Open Source)
Community Edition
Full-featured open source WAF
- Complete WAF engine
- Apache/Nginx/IIS support
- OWASP CRS compatible
- Unlimited customization
Commercial Support
Vendor-provided support and management
- Professional support
- Rule updates
- Management interface
- SLA guarantees
Our Verdict
ModSecurity remains a viable choice for organizations with the expertise to operate it. Its combination of zero licensing cost and unlimited flexibility makes it attractive for security teams who want full control over their WAF configuration.
However, ModSecurity is not a set-and-forget solution. Success requires dedicated staff time for initial tuning, ongoing maintenance, and rule updates. Organizations without WAF expertise should consider managed alternatives unless learning is part of their goal.
Our verdict: Best option for security teams with WAF expertise who want maximum control at minimum cost. Not recommended for those seeking simplicity.
CVE Coverage
ModSecurity Open Source WAF can detect and block attacks matching 87K+ known CVEs based on its supported rule sets.
Coverage by Attack Type
Latest Blockable CVEs
| CVE | Severity |
|---|---|
| CVE-2026-4510 | MEDIUM |
| CVE-2026-4161 | MEDIUM |
| CVE-2026-4087 | MEDIUM |
| CVE-2026-4086 | MEDIUM |
| CVE-2026-4084 | MEDIUM |
| CVE-2026-4077 | MEDIUM |
| CVE-2026-4072 | MEDIUM |
| CVE-2026-4069 | MEDIUM |
| CVE-2026-4067 | MEDIUM |
| CVE-2026-4022 | MEDIUM |
Frequently Asked Questions
Is ModSecurity still maintained?
Yes, ModSecurity continues to be maintained as a community project. ModSecurity 3.x (libmodsecurity) is actively developed on GitHub. The OWASP Core Rule Set, which most deployments use, is also actively maintained with regular updates to address new threats.
ModSecurity vs cloud WAF - which is better?
It depends on your resources and requirements. Cloud WAFs (Cloudflare, AWS WAF) are easier to deploy and maintain but cost money and provide less customization. ModSecurity is free and infinitely customizable but requires expertise. Most modern deployments favor cloud WAFs unless specific customization or cost requirements dictate otherwise.
What's the difference between ModSecurity 2.x and 3.x?
ModSecurity 2.x runs as an Apache module only. ModSecurity 3.x (libmodsecurity) is a standalone library that can integrate with any platform via connectors. There are connectors for Nginx, Apache, and other platforms. Version 3.x is recommended for new deployments, especially with Nginx.
Ready to try ModSecurity Open Source WAF?
Start with the free tier and upgrade as you grow.