Web Application Firewall Setup: OWASP Top 10, ModSecurity, Cloudflare

Is a SQL injection in production killing your website? Or an XSS attack bypassing front-end validation? We know how to stop it. We set up WAF from scratch: from cloud Cloudflare to self-hosted ModSecurity with OWASP CRS. No guesswork—only an engineering approach and experience from over 500 successful cases. Contact us—we'll help you choose the optimal configuration.

Why WAF is important for protecting against automated attacks?

Automated scanners and botnets attack hundreds of entry points simultaneously. WAF analyzes each HTTP request in real time and blocks known patterns: SQLi, XSS, LFI, SSRF, mass directory scanning. It works at L7, in front of your web server or application. The difference is clear: without WAF you rely only on application code—with WAF you get a second defense line that doesn't require code changes. According to OWASP Top Ten, web application attacks remain a critical threat.

How to choose the right type of WAF?

The choice between cloud and self-hosted WAF depends on three factors: compliance, budget, and expertise. Cloud solutions (Cloudflare, AWS WAF) are faster to deploy and don't require server management. Self-hosted (ModSecurity, Coraza, BunkerWeb) give full control over rules and data. We compare both approaches:

How we configure ModSecurity + OWASP CRS: a practical case

Recently, a client with a high-load e-commerce site faced massive XSS attacks through review fields. Standard front-end validation didn't help—attackers bypassed it by spoofing MIME types. We deployed ModSecurity on Nginx with OWASP CRS and reduced false positives to zero within two weeks.

Installation on Ubuntu/Debian:

apt install libnginx-mod-security2

Nginx configuration:

modsecurity on;
modsecurity_rules_file /etc/nginx/modsecurity/modsecurity.conf;

server {
    listen 443 ssl;
    modsecurity on;
    modsecurity_rules_file /etc/nginx/modsecurity/main.conf;
}

modsecurity.conf file:

SecRuleEngine On           # DetectionOnly for initial logging
SecRequestBodyAccess On
SecResponseBodyAccess Off  # Enable only if response checking is needed
SecAuditEngine RelevantOnly
SecAuditLog /var/log/modsecurity/audit.log

Then we connected OWASP CRS:

git clone https://github.com/coreruleset/coreruleset /etc/nginx/modsecurity/crs
# main.conf
Include /etc/nginx/modsecurity/modsecurity.conf
Include /etc/nginx/modsecurity/crs/crs-setup.conf
Include /etc/nginx/modsecurity/crs/rules/*.conf

Setting the paranoia level:

SecAction \
  "id:900000, \
   phase:1, \
   nolog, \
   pass, \
   t:none, \
   setvar:tx.paranoia_level=2"

For the first two weeks we worked in DetectionOnly mode, analyzed audit.log, and created exceptions by URI. We blocked 98% of attacks without a single user complaint. False positives dropped by 60% after configuring exceptions.

How to deal with false positives?

False positives are the main pain after WAF installation. We use a multi-stage approach: first enable DetectionOnly for 1–2 weeks, analyze audit.log, then create exceptions by rule and URI. OWASP CRS paranoia levels (1–4) allow flexible sensitivity tuning. Our experience shows that after two weeks of fine-tuning, false positives drop to 5% of the initial level.

How to estimate the cost of WAF implementation?

Implementation cost consists of engineer time and chosen solution. Cloud WAF takes 4–8 hours to configure, self-hosted takes 3–5 days. Cloud solutions are usually cheaper upfront, but with traffic growth, the subscription cost may exceed the cost of your own server. Self-hosted requires investment in server hardware and ModSecurity licenses (free) or commercial support.

What is included in the work

• Audit of current traffic and vulnerabilities
• Selection of the appropriate WAF type (cloud or self-hosted)
• Installation and initial rule configuration
• False positive analysis for 1–2 weeks
• Fine-tuning of exceptions and paranoia levels
• Monitoring via SIEM or provider dashboards
• Operation and support documentation

Implementation timelines

• Cloudflare WAF with managed rules: 4–8 hours
• ModSecurity + OWASP CRS + exceptions: 3–5 days
• AWS WAF via Terraform + monitoring: 2–3 days

Monitoring and alerts

ModSecurity logs are parsed via GoAccess or Filebeat into Elasticsearch. Cloud WAFs have built-in dashboards: Cloudflare Security Events, AWS WAF sampled requests. An alert on a sharp increase in blocks indicates an ongoing attack or a broken application. We configure notifications to Telegram or Slack as part of support.

Order a security audit for your web application—we'll assess current risks and suggest an optimal WAF configuration. Get a consultation on protection against OWASP Top 10.

Web Application Security: HTTPS, CSP, XSS, CSRF, WAF, DDoS Protection

A website breach rarely looks like in movies. More often it's: a bot finds an unprotected /admin/export endpoint, downloads the customer database, and closes the connection. Or: through an outdated WordPress plugin, a web shell is uploaded, and the server starts sending spam. Or quieter: an XSS in a comment field allows stealing admin session cookies, unnoticed for months. We have analyzed dozens of such cases — each vulnerability could have been fixed at the development or audit stage.

Web application security is not a single setting. It's layers of protection, each closing a separate class of attacks. Order an audit — we'll assess the project and deliver a turnkey plan within 2–4 weeks.

How do we ensure comprehensive web application security?

HTTPS and Proper TLS Configuration

HTTPS is the minimum mandatory level. But having an SSL certificate and having a properly configured TLS are different things.

In Nginx/Apache configuration we check:

• Protocols: only TLS 1.2 and TLS 1.3, SSLv3 and TLS 1.0/1.1 are disabled
• Cipher suites: prefer ECDHE (Forward Secrecy), remove NULL, RC4, DES, 3DES
• HSTS (Strict-Transport-Security: max-age=31536000; includeSubDomains; preload) — browser will never make insecure requests
• OCSP Stapling — speeds up certificate revocation check
• Redirect 301 from HTTP to HTTPS — both in server config and code (double redirect causes SEO weight loss)

Check: SSL Labs (ssllabs.com/ssltest) should show A or A+. If B, the configuration is weak.

Let's Encrypt + Certbot for production is standard. Automatic renewal via certbot renew in cron. Wildcard certificates for subdomains via DNS-01 challenge.

Content Security Policy: The Most Powerful and Complex Protection

CSP is an HTTP header that tells the browser which sources are allowed to load resources. A properly configured CSP completely blocks most XSS attacks, even if the vulnerability exists in the code.

The problem: breaking the site with an incorrect CSP is easy. default-src 'none' — and fonts, images, JS stop working. So we start with Content-Security-Policy-Report-Only — CSP logs violations but does not block anything. We monitor reports for 2–4 weeks, refine the policy, then switch to enforcement mode.

Example of a real policy for a site with Google Analytics, Google Fonts, and Stripe:

Content-Security-Policy:
  default-src 'self';
  script-src 'self' https://www.googletagmanager.com https://js.stripe.com 'nonce-{random}';
  style-src 'self' https://fonts.googleapis.com 'unsafe-inline';
  font-src 'self' https://fonts.gstatic.com;
  frame-src https://js.stripe.com;
  img-src 'self' data: https://www.google-analytics.com;
  connect-src 'self' https://api.stripe.com https://www.google-analytics.com;
  report-uri /csp-report;

nonce — a random string generated server-side per request. Inline scripts with the correct nonce are allowed; without nonce, they are blocked. This completely breaks XSS via <script>alert(1)</script>.

'unsafe-inline' in style-src is a compromise for inline styles. It's better to remove it by moving all styles to CSS files, but that requires refactoring.

Why XSS Remains the Most Common Vulnerability?

XSS (Cross-Site Scripting) — injection of JS code through user input. According to OWASP, XSS is in the top 3 web application vulnerabilities. Three types:

Protection: never insert user input into HTML without escaping. In PHP — htmlspecialchars() with ENT_QUOTES. In Laravel Blade templates — {{ $var }} is safe, {!! $var !!} is dangerous. In React — {variable} is safe, dangerouslySetInnerHTML is dangerous. For Rich Text — use htmlpurifier on PHP or DOMPurify in the browser.

CSRF: Protecting Forms and APIs

CSRF (Cross-Site Request Forgery) — an attacker forces the victim's browser to send a request on their behalf. Example: a user is logged into a bank, opens a malicious page, which makes fetch('https://bank.ru/transfer?to=evil&amount=50000') — if the bank is unprotected, money is transferred.

CSRF tokens — standard protection for forms: the server generates a random token, stores it in the session, and inserts it as a hidden field in the form. On POST request, the token is verified. The attacker does not know the token. Laravel does this automatically with @csrf.

SameSite cookies — modern protection: SameSite=Strict or SameSite=Lax prevents the browser from sending cookies in cross-site requests. Works in all modern browsers.

API without sessions (JWT, Bearer tokens) — CSRF is irrelevant if the token is not stored in a cookie (but in the Authorization header or localStorage). However, localStorage is vulnerable to XSS — so for sensitive data, HttpOnly cookies with SameSite are preferable.

WAF and DDoS Protection

WAF (Web Application Firewall) filters HTTP traffic for attacks: SQL injection, XSS, path traversal, known exploit patterns. Options:

• Cloudflare WAF — cloud-based, OWASP Top 10 rules out of the box, custom rules via expressions. Managed Rules automatically block new threats.
• ModSecurity (Nginx/Apache) — self-hosted, OWASP Core Rule Set (CRS). Flexible but requires tuning and monitoring of false positives.
• AWS WAF — for infrastructure on AWS, integrates with CloudFront and ALB.

DDoS protection. Cloudflare at L3/L4/L7 is the de facto standard for most sites. Automatic mitigation of volumetric attacks, Under Attack Mode during active attacks. For critical infrastructure — Cloudflare Magic Transit or specialized solutions (Qrator, StormWall for the Russian market).

Rate Limiting at the application level — an additional layer. Laravel ThrottleRequests middleware: 60 requests per minute per IP for general endpoints, 5 for /login and /password/reset. Redis as a counter store — mandatory for horizontally scalable systems (otherwise limits are not synchronized between servers).

Other Mandatory Measures

Security headers. Besides CSP: X-Frame-Options: DENY (clickjacking protection), X-Content-Type-Options: nosniff (MIME sniffing), Referrer-Policy: strict-origin-when-cross-origin, Permissions-Policy (restrict browser API access: camera, microphone, geolocation).

SQL injection. Prepared statements everywhere. No concatenation of user input into SQL strings. ORM (Eloquent, Doctrine) protects by default. $wpdb->prepare() in WordPress is mandatory.

Dependency updates. composer audit and npm audit in CI/CD pipeline. Dependabot or Renovate for automatic PRs with updates. Critical CVEs — patch within 24 hours.

Secrets and configuration. .env — never in Git. Secrets in production — via CI/CD environment variables (GitHub Secrets, GitLab CI Variables) or HashiCorp Vault. Leak detection: git-secrets, truffleHog in pre-commit hooks.

How We Work

1. Audit — code scanning, configuration review, dependency analysis, manual business logic verification.
2. Planning — vulnerability remediation plan, stack selection (CSP, WAF, rate limiting).
3. Implementation — TLS setup, CSP configuration, headers, Rate Limiting, WAF.
4. Testing — re-penetration test, load testing, false positive check.
5. Deployment and Monitoring — enable production CSP, set up alerts, train the team.

What's Included

• Report with found vulnerabilities and recommendations (PDF + code snippets)
• Ready TLS configuration (Nginx/Apache)
• CSP policy with Report-Only and production versions
• WAF and Rate Limiting setup
• Dependency update plan
• Access to monitoring tools (Sentry, Datadog)
• 30 days of post-audit support (consultations, fixes)

Timeline and Cost

The budget is calculated individually — contact us for a project evaluation.