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 111K+ known CVEs based on its supported rule sets.
Coverage by Attack Type
Latest Blockable CVEs
| CVE | Severity |
|---|---|
| CVE-2026-49294 | UNKNOWN |
| CVE-2026-20262 | MEDIUM |
| CVE-2026-9863 | UNKNOWN |
| CVE-2026-9862 | UNKNOWN |
| CVE-2025-15659 | UNKNOWN |
| CVE-2025-15658 | UNKNOWN |
| CVE-2026-52704 | UNKNOWN |
| CVE-2019-25746 | HIGH |
| CVE-2018-25436 | CRITICAL |
| CVE-2016-20084 | HIGH |
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.
Is ModSecurity end of life?
No. ModSecurity is not end of life, but its status has changed. In January 2024, Trustwave transferred ModSecurity to the OWASP Foundation as a community project. Trustwave discontinued their commercial ModSecurity products and rule feeds. The open source project (ModSecurity v3 / libmodsecurity) is still maintained on GitHub with bug fixes and security patches, but the pace of new feature development is slower than before. The OWASP CRS, which provides the actual protection rules, remains actively maintained with regular releases. For new deployments, consider evaluating Coraza as a modern alternative that runs the same CRS rules.
What are the best ModSecurity alternatives?
The most direct alternative is Coraza, an open source WAF written in Go that is fully compatible with ModSecurity's SecLang rule language. Your existing CRS rules work without modification. Other alternatives depend on what you need:
- Coraza: drop-in replacement, same rules, modern Go implementation, better for Caddy/Traefik/Kubernetes
- BunkerWeb: wraps ModSecurity/CRS with a web UI and Docker-first deployment
- CrowdSec: different approach (crowd-sourced threat intelligence), can complement rather than replace ModSecurity
- Cloud WAFs (Cloudflare, AWS WAF, Fastly): managed services, no self-hosting, but less customization and ongoing costs
If you want to keep using your existing SecLang rules and CRS configuration, Coraza is the closest migration path.
Does ModSecurity work with HAProxy?
Not natively. ModSecurity has official connectors for Apache (mod_security2), Nginx (ModSecurity-nginx), and IIS. There is no official HAProxy connector. If you need a WAF with HAProxy, Coraza has a HAProxy plugin (coraza-spoa) that uses HAProxy's SPOE protocol and supports the same SecLang rules. Alternatively, you can run ModSecurity on a separate Nginx instance as a reverse proxy behind HAProxy.
How do I install ModSecurity with Nginx?
ModSecurity integrates with Nginx through the ModSecurity-nginx connector, which links against libmodsecurity (ModSecurity v3). The typical steps are:
- Install libmodsecurity (build from source or use a package like libnginx-mod-http-modsecurity on Ubuntu/Debian)
- Compile or install the ModSecurity-nginx connector module
- Enable ModSecurity in your Nginx config with
modsecurity on; - Point to your rules file with
modsecurity_rules_file - Install and configure the OWASP CRS for actual protection rules
On Ubuntu 24.04+, the libnginx-mod-http-modsecurity package simplifies this. On other platforms, building from source is common but requires libxml2, libpcre, and other C dependencies.
Can I use ModSecurity with Caddy?
Not directly. ModSecurity does not have a Caddy plugin or connector. If you use Caddy as your web server or reverse proxy, look at Coraza instead. The coraza-caddy plugin provides WAF protection with full CRS support and is the most popular Coraza integration. Since Coraza speaks the same SecLang rule language, your existing ModSecurity rules will work with it.
Does ModSecurity have a GUI or dashboard?
ModSecurity itself has no built-in management UI. Configuration is done through text files (modsecurity.conf and CRS rule files). For a visual interface, third-party options include:
- BunkerWeb: wraps ModSecurity/CRS with a full web dashboard
- WAF2Py: open source ModSecurity management interface
- ELK stack or Grafana: for visualizing ModSecurity audit logs and blocked requests
- Commercial distributions from vendors that bundle ModSecurity with management tools
If GUI-based management is a priority, a managed cloud WAF or BunkerWeb may be a better fit than raw ModSecurity.
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