The positive-security alternative to ModSecurity
ModSecurity is the open-source rules engine behind a lot of WAFs. It works, and it is famous for two things: the OWASP Core Rule Set, and the false positives that come with tuning it.
Two different models
ModSecurity is pure signature matching, usually run with the OWASP Core Rule Set. It is free and powerful, and it is well known for being high-maintenance and false-positive-prone, with no model of your specific application.
Nemesis Shield is a positive-security platform that spans the whole request path. A one-line, open-source SDK (Sentinel) learns each app, API and LLM's own normal behavior per tenant and blocks the deviations a signature ruleset never sees: IDOR/BOLA, broken auth, business-logic abuse and zero-days. Nemesis Edge adds a per-tenant protective-DNS and optional inline-proxy layer at the network edge, running in front of or on top of your existing CDN, and it all correlates into one view. Free tier, observe-first, about two minutes to protect an app.
Side by side
| ModSecurity | Nemesis Shield | |
|---|---|---|
| Detection model | Regex signatures (OWASP CRS), hand-tuned | Learns your app's own normal, no rule writing |
| False positives | The main operational cost; tuning is constant | Observe-first, per-tenant baseline, approve/deny review before enforce |
| Logic attacks (IDOR/BOLA) | Not addressed by signatures | Caught as deviations from the baseline |
| Effort | Deploy, tune rules, maintain forever | One line, learn, enforce |
When to choose which
If you want a free, self-hosted rules engine and you have the team to maintain the ruleset, ModSecurity is a solid open-source option.
If you would rather the app teach the WAF what normal is than hand-tune regexes forever, that is Nemesis Shield. The SDKs are open source too.
Questions
Is Nemesis Shield a ModSecurity alternative?
Yes, and often a complement. ModSecurity and Nemesis Shield solve overlapping but different problems: ModSecurity works at the level it was designed for, and Nemesis adds a positive-security layer that learns your app's own per-tenant behavior and blocks the logic-level attacks (IDOR/BOLA, broken auth, business-logic abuse) that a signature ruleset is not built to see.
Can I run Nemesis Shield together with ModSecurity?
Yes. Nemesis is a one-line SDK inside your app (and an optional edge layer), so it runs happily behind or on top of ModSecurity. Many teams keep ModSecurity for what it is good at and add Nemesis for the application-logic layer.
What does Nemesis catch that a signature WAF does not?
Attacks that are well-formed. A request for an object that is not yours (IDOR/BOLA), a broken-auth flow, or business-logic abuse has no bad pattern to match, so a signature engine passes it. Nemesis flags it because it deviates from the app's learned normal, per tenant.
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