Looking for a free, open-source way to protect your web applications from attacks like XSS, SQLi, and RCE? Here are five top-tier WAFs you can deploy today. A Web Application Firewall (WAF) sits between users and your web server,…

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Looking for a free, open-source way to protect your web applications from attacks like XSS, SQLi, and RCE? Here are five top-tier WAFs you can deploy today.

A Web Application Firewall (WAF) sits between users and your web server, analyzing incoming HTTP requests and blocking malicious payloads before they reach your application.

WAFs are commonly used to defend against:

SQL Injection (SQLi)

Cross-Site Scripting (XSS)

Cross-Site Request Forgery (CSRF)

Command injection

DDoS and automated bot attacks

In this post, we’ll focus on open-source WAFs—those you can self-host, audit, customize, and scale. Whether you're securing a personal project or an enterprise-grade app, these WAFs offer powerful protection without a recurring license fee.

Why Choose an Open Source WAF?

Free to use and deploy

Privacy-respecting — no need to route traffic through third-party clouds

Highly customizable — tweak rules, loggers, detection logic

Better control over updates, integrations, and architecture

Of course, you’ll need to configure and maintain them yourself—or hire someone to do it. But for many developers and teams, that tradeoff is well worth it.

The 5 Best Open Source WAFs

1. SafeLine

GitHub →

License: GPL-3.0

Languages: Go, C++, Perl, Lua

SafeLine is a high-performance reverse proxy WAF built on Nginx and maintained by Chaitin Tech. It detects and blocks a wide range of attacks: SQLi, OS command injection, CRLF injection, and more. It’s especially strong in anti-bot protection through:

HTML/JS obfuscation

IP-based rate limiting

Semantic-aware detection engine (less reliance on rules)

You also get a modern web UI for traffic insights, real-time rule management, and monitoring — making SafeLine beginner-friendly and production-ready.

Deployment: Docker, Bash scripts

Bonus: Web dashboard included

2. open-appsec

GitHub →

License: Apache 2.0

Language: C++

Open-appsec uses machine learning models (supervised + unsupervised) to detect OWASP Top 10 vulnerabilities and zero-day attacks. It integrates with:

Kubernetes Ingress

NGINX

API gateways

It deeply inspects HTTP payloads (including JSON/XML) and applies behavior-based detection. However, due to its AI capabilities, it can be resource-intensive.

Ideal for: AI-driven environments with high variability

Note: No UI, CLI-based and YAML-heavy

3. ModSecurity

GitHub →

License: Apache-2.0

Language: C++

ModSecurity is a veteran in the WAF world. It supports Apache, NGINX, and IIS, and powers many commercial WAFs. The v3 engine (libmodsecurity) decouples from Apache and improves performance.

Key strengths:

Compatible with OWASP Core Rule Set

Event-based detection engine

Works well with command-line logging and alerting

Weakness: No UI, outdated documentation, steeper learning curve

Best for: Power users who want total control

4. BunkerWeb

GitHub →

License: AGPL-3.0

Language: Python

BunkerWeb is a Dockerized WAF built on NGINX. It supports:

TLS hardening + Let’s Encrypt auto-cert

Built-in ModSecurity integration

Security headers

Plugin ecosystem (e.g., ClamAV antivirus)

It features a web UI and supports deployment on Docker, Kubernetes, Azure, and Swarm. It also offers a cloud-based commercial option similar to Cloudflare WAF.

Strength: Highly configurable via plugins

Ideal for: Teams wanting UI + modular security controls

5. Coraza

GitHub →

License: Apache-2.0

Language: Go

Coraza is a modern, lightweight WAF written in Go that supports ModSecurity’s SecLang and OWASP Core Rule Set. It’s designed to be fast and embeddable, making it perfect for cloud-native and microservice environments.

Coraza doesn’t ship with a UI, but you can customize loggers and integrations easily.

Drop-in replacement for ModSecurity

Works well with reverse proxies and sidecars

Final Thoughts

Open source WAFs offer a powerful and flexible alternative to proprietary services. While they may require a bit more setup, they give you control, transparency, and strong security with no vendor lock-in.

Remember: A WAF is just one part of a complete security strategy. Regular audits, secure coding, and patching are just as critical.

Join the SafeLine Community

If you continue to experience issues, feel free to contact SafeLine support for further assistance.

GitHub Repository

Official Docs

Discord Community

Original article: https://fosspost.org/open-source-waf-web-application-firewalls

CTI Threat Relationship Graph6 Knoten / 5 Relationen

CVE / Incident Software MITRE ATT&CK CWE Weakness IoC

IR-PLAYBOOK-RCEHIGH

Schritte anzeigen

SOC Incident Playbook: Remote Code Execution (RCE) Defense

WAF MitigationSofort

Virtuelles Patchen am Reverse Proxy / WAF für gefährdete URL-Pfade und Payloads aktivieren.

SecRule REQUEST_URI "@rx ..." "id:1001,phase:1,deny,status:403"

Web Shell ScanSofort

Web-Root auf neu angelegte Scripts, anomal modifizierte Dateien und Persistence scannen.

find /var/www -type f -name "*.php" -mmin -120

Outbound FilteringSofort

Ausgehenden Datenverkehr (Reverse Shells zu unbekannten IPs/Ports) blockieren.

ss -tunp | grep -E ":(4444|1337|8080|9001)"

Vendor Patching

Hersteller-Update in Staging validieren und schnellstmöglich in Produktion ausrollen.

apt update && apt --only-upgrade install <pkg>

1-Click Detection Engineering: Multi-Dialect SIEM Rules5 Formate

Regeln anzeigen

Syntax validiert (0 Fehler)

title: Detect Exploitation - Top 5 Open Source WAFs to Secure Your Web Apps in 2025
id: c5e17afb-98c6-4e27-b334-42e7523ab8d7
status: experimental
description: Automatisch generierte SIEM-Erkennungsregel basierend auf CTI Intelligence
references:
  - https://tsecurity.de/
author: iShareStuff CTI Automated Detection Engine
date: 2026-09-24
logsource:
  category: network_connection
  product: any
detection:
  selection:
      CommandLine|contains:
        - 'exploit'
  condition: selection
falsepositives:
  - Legitime administrative Zugriffe oder Penetrationstests
level: high
tags:
  - attack.initial_access
  - attack.t1190

Syntax validiert (0 Fehler)

rule CTI_Threat_Indicator {
    meta:
        author = "iShareStuff CTI Automated Detection Engine"
        date = "2026-09-24"
        description = "YARA Signature for "
    strings:
        $str = "Top 5 Open Source WAFs to Secu" ascii wide
    condition:
        any of them
}

Syntax validiert (0 Fehler)

index=security sourcetype IN ("cisco:asa", "pan:traffic", "zeek_conn", "suricata", "WinEventLog:Security")
("Top 5 Open Source WAFs to Secure Your We")
| stats count earliest(_time) as first_seen latest(_time) as last_seen by src_ip, dest_ip, dest_host, signature
| eval first_seen=strftime(first_seen, "%Y-%m-%d %H:%M:%S"), last_seen=strftime(last_seen, "%Y-%m-%d %H:%M:%S")
| sort - count

Syntax validiert (0 Fehler)

message: "*Top 5 Open Source WAFs to Secure Your We*"

Syntax validiert (0 Fehler)

CommonSecurityLog
| where Message has "Top 5 Open Source WAFs to Secure Your We"
| summarize EventCount = count(), FirstSeen = min(TimeGenerated), LastSeen = max(TimeGenerated) by SourceIP, DestinationIP, DestinationPort, Activity
| extend DetectionRule = "iShareStuff-CTI-Compiled"
| sort by EventCount desc

🎯

MITRE ATT&CK Matrix Navigator 14 Taktiken

Identifiziert: T1190Exploit Public-Facing Application

Reconnaissance

Resource Development

Initial Access

Execution

Persistence

Privilege Escalation

Defense Evasion

Credential Access

Discovery

Lateral Movement

Collection

Command and Control

Exfiltration

Impact

💡 Tipp: Klicken Sie auf eine TTP, um Gegenmaßnahmen und SIEM-Erkennungsregeln anzuzeigen.Enterprise Matrix v14.1

🚀 Auf tsecurity.de entdecken

◀ VORHERIGER BEITRAG 16 Min

new extra

Sichere Programmierung

NÄCHSTER BEITRAG 9 Min

HTTP Request Processing with Zero-Copy Optimization(4012)

Sichere ProgrammierungWeiterlesen ▶

Blättern: Pfeiltasten [ ← ] [ → ] · Tasten j / k · mobil: Wischen

Fokus-Vektor:

Kognitive Analyse für identifizierte Bedrohung: Erhöhte Bedrohungslage im Bereich Top 5 Open Source WAFs to Secure Your We.... Basierend auf 368k Vektor-Korrelationen werden sofortige Isolationsmaßnahmen für betroffene Endpunkte empfohlen.

🛡️ Angriffsfläche & Exposure

Netzwerk/Remote-Zugriff ohne Vorauthentifizierung möglich.

⚡ Empfohlene Sofortmaßnahmen

1. Perimeter-Inspektion: Relevante Portfreigaben und exponierte Endpunkte unverzüglich scannen.
2. Patch-Applikation: Hersteller-Hotfix einspielen oder betroffene Daemons in isolierte DMZ-Segmente überführen.
3. Telemetrie & EDR-Alerts: Prozessaufrufe und Child-Processes auf anomale Shell-Spawns überwachen.

🔗 Semantisch verwandte Zero-Days MariaDB 11.7 VEC

Schnell-Prompts für Analysten

⚠️ DEFANGED SANDBOX VIEW (tsecurity.de): Alle Netzwerkindikatoren und URLs wurden neutralisiert (2 Indikatoren entschärft). Nur zur defensiven Analyse!

Format: python

#!/usr/bin/env python3
# Exploit Title: PoC for Target
import socket, sys
target = '192[.]168[.]1[.]10'
url = 'hxxp://target[.]local/vuln'
s = socket.socket()
s.connect((target, 80))
s.send(b'GET / HTTP/1.1\r\nHost: target.local\r\n\r\n')