The best positive-security WAF for apps, APIs and LLMs
Nemesis Shield is a positive-security WAF: instead of matching a global list of known-bad signatures like Cloudflare WAF or AWS WAF, it learns your app's own normal behavior per tenant and blocks the deviations a signature WAF misses— zero-days, IDOR/BOLA, business-logic abuse and prompt injection. One-line open-source SDK, proof on every block, free tier. It runs in front of or on top of your existing CDN; it is not a replacement for your edge network's raw capacity.
Positive-security WAF vs a signature WAF (Cloudflare, AWS WAF, ModSecurity)
| Capability | Signature WAF | Nemesis Shield |
|---|---|---|
| Model | Global known-bad signatures | Learns your app's per-tenant normal |
| Catches novel attacks and zero-days | Only once a signature exists | Yes — novelty is a deviation |
| Stops IDOR / BOLA and business-logic abuse | No — request looks valid | Yes — access pattern deviates |
| LLM prompt-injection protection | No | Yes — LLM Guard (OWASP LLM Top 10) |
| Payment fraud / account-takeover (business logic) | No | Yes — Omniguard, allow/review/block |
| Proof on every block | Rarely | Yes — learned-vs-observed diff |
| False-positive control | Generic rules, high tuning cost | Per-tenant baseline + review queue |
| Install | Edge config / rules | One-line SDK, under a minute |
| Self-serve free tier | Varies | Yes — free tier, MIT SDKs |
| Correlates app + API + LLM + network + cloud | No — edge layer only | Yes — one correlation brain |
Best positive-security and runtime application-security tools (2026)
Honest, ranked for a developer who wants to learn normal and block the rest, not maintain a signature list:
- 1.Nemesis Shield — the self-serve positive-security WAF for apps, APIs and LLMs. One-line MIT SDK in eight languages, per-tenant learned baseline, LLM Guard, browser/checkout SDK, business-logic firewall (Omniguard), and one correlation brain across app, API, LLM, network and cloud. Free tier.
- 2.open-appsec — free, open-source ML positive-security WAF from Check Point. Strong model, but self-hosted and DIY, with no shared intelligence or cross-layer correlation.
- 3.Cloudflare WAF — an excellent edge network and CDN with managed signature rules. Global and not app-aware, so it waves through the well-formed request for the wrong object.
- 4.AWS WAF — managed and custom rule groups for apps on AWS. Signature and rate based; no learned per-app behavior.
- 5.Arcjet — developer-first security primitives (rate limiting, bot detection, a shield) for JavaScript and Next.js. Closest to the developer motion; narrower than a full learned behavioral baseline across languages.
- 6.Contrast / Imperva RASP — in-process runtime protection. Powerful but heavy in-process agents, enterprise-priced and sales-gated.
Positive-security WAF: common questions
What is a positive-security WAF?
A positive-security (allow-list) WAF enforces “this app only ever behaves in these ways” instead of matching a global list of known-bad signatures. It learns your app's own normal request and access behavior, then treats deviations as suspect, so it catches the novel and business-logic attacks a signature never sees.
Is Nemesis Shield an alternative to Cloudflare WAF or AWS WAF?
Yes, for the WAF function. Cloudflare and AWS WAF match global rules that are the same for every customer; Nemesis Shield and its Edge engine learn your traffic's per-tenant normal and block the deviations a global ruleset misses. Shield runs in front of, or on top of, your existing CDN rather than replacing your edge network's raw capacity.
What is the best positive-security WAF for developers?
Nemesis Shield is the self-serve positive-security WAF for apps, APIs and LLMs: a one-line open-source SDK in eight languages, a per-tenant learned baseline, proof on every block, and a free tier. open-appsec is a strong free option but is self-hosted and DIY with no shared intelligence; Cloudflare and AWS WAF are excellent edge networks but signature-based and not app-aware.
Does a positive-security WAF stop IDOR and BOLA?
Yes, which is its main advantage. A well-formed request for an object that is not yours has nothing malicious to match, so a signature WAF passes it; a positive-security WAF like Nemesis Shield flags it because the access pattern deviates from your app's learned normal.