A WAF inspects HTTP traffic and blocks SQLi, XSS, and other patterns. Can be cloud-based or on-prem. Tune rules to avoid blocking legitimate traffic; use logging and mode (detect vs block) during rollout.
What a WAF does
- Inspection: Analyzes HTTP/HTTPS requests and responses. Looks for attack signatures (SQL injection, XSS, path traversal, etc.) and can enforce limits (rate, payload size).
- Actions: Block, challenge (e.g. CAPTCHA), or allow. Often configurable per rule or per URI.
- Placement: In front of your app—as a cloud service (CDN/WAF) or as an on-prem/self-hosted component (e.g. ModSecurity, commercial WAF).
Rules and tuning
- Default rules: Most WAFs ship with rule sets (e.g. OWASP Core Rule Set). They reduce common attacks but can cause false positives (blocking legitimate requests).
- Tune: Disable or relax rules that break your app. Use allowlists for known-good paths or params. Prefer tuning by exception rather than turning off whole categories.
- Detect vs block: During rollout, run in "detect" or "report-only" mode. Log what would be blocked; fix false positives; then switch to block mode. Revisit after major app changes.
Operations
- Logging: Send WAF logs to your SIEM or logging stack. Use them for incident response and tuning. Alert on critical rule hits or sudden spike in blocks.
- Updates: Rule sets get updates for new CVEs and attack patterns. Plan for testing and deployment of rule updates so you do not break the app or leave gaps.
- Performance: WAF adds latency. Measure and optimize; use edge WAF when possible to keep latency low.
Summary
A WAF inspects HTTP traffic and blocks SQLi, XSS, and other patterns. Can be cloud or on-prem. Tune rules to avoid false positives; use detect mode during rollout; log and update rules regularly.
