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Open Source WAF / WAF Engine / Rule-based WAF

ModSecurity WAF

ModSecurity is a widely known open-source WAF engine and a common baseline for rule-based web application firewall deployments.

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Quick answer

Should you shortlist ModSecurity?

ModSecurity is most relevant for Rule-based detection and Existing CRS users. Validate this main constraint before committing to a production design: Rule tuning can be noisy.

Deployment
Nginx, Apache, IIS
Pricing
Free
License
Open source

Data card

Pricing
Free
License
Open source
Deployment
Nginx, Apache, IIS, Reverse Proxy
Integrations
OWASP CRS, Nginx, Apache
Last checked
2026-05-30

Best fit

  • Rule-based detection
  • Existing CRS users
  • Legacy WAF stacks

Potential limitations

  • Rule tuning can be noisy
  • Operational complexity depends on connector and rule set quality

WAFWiki read

Long-running open-source WAF engine.

This profile is written for evaluation rather than promotion. Use it to understand where ModSecurity fits, which assumptions need validation, and which alternatives deserve side-by-side testing.

Evaluation checklist

  • Validate connector compatibility for the exact NGINX, Apache, or IIS path you plan to run.
  • Start with OWASP CRS in detection-only mode and tune paranoia level deliberately.
  • Track audit log volume, false positives, exclusions, and rule IDs during normal user workflows.
  • Document how CRS updates, local exclusions, and emergency rule disables will be reviewed.

Feature snapshot

ModSecurity capabilities to verify

Transaction inspectionRule engineCRS ecosystem

Comparisons

ModSecurity alternatives and versus pages

SafeLine vs ModSecurityModSecurity vs CorazaF5 WAF for NGINX vs ModSecurity

WAFWiki lab evidence

ModSecurity results observed in the local test stack

ModSecurity vs Coraza Docker Test: 20 Request ResultsOriginal ModSecurity vs Coraza Docker comparison using the same OWASP CRS 4.25.0, upstream, and 20 HTTP decisions across clean, SQLi, XSS, query, and JSON cases.WAF JSON Body Test: ModSecurity vs CorazaHands-on JSON request-body test showing how ModSecurity and Coraza handled one clean body plus controlled SQLi-like and XSS-like fields under OWASP CRS 4.25.0.OWASP CRS False Positive Test: 12 Clean RequestsClean-traffic regression test for ModSecurity and Coraza with 12 HTTP 200 decisions, six input patterns, zero blocking mismatches, and one repeatable numeric Host warning.ModSecurity CRS Docker Smoke TestA reproducible local smoke test for OWASP CRS with ModSecurity and NGINX, covering clean traffic, a SQLi-like lab request, evidence logs, and rollout caveats.

FAQ

What is ModSecurity best for?

ModSecurity is commonly evaluated for Rule-based detection, Existing CRS users, Legacy WAF stacks.

Is ModSecurity free?

ModSecurity pricing path: Free. Always verify current pricing on the official website.

Sources