Frontend Security Csp And Xss Hardening
Use When
- Internet-facing UI with rich user content
- Security review flagged XSS or CSP gaps
Workflow
- Define CSP policy per environment with nonce or hash strategy
- Sanitize untrusted HTML and URL inputs
- Restrict inline scripts and dangerous DOM APIs
- Audit third-party scripts and dependencies
- Validate security headers at edge and app layers
Required Checks
- CSP violations monitored with actionable alerts
- Dangerous HTML rendering paths are eliminated or sanitized
- Clickjacking protections enabled
- Dependency vulnerability scan in CI
Decision Framework
- Default deny for script sources unless explicitly approved
- Never trust client-side sanitization alone for persisted content
- Use Subresource Integrity for external assets when possible
- Separate admin and user rendering paths
Common Rationalizations And Rebuttals
- "CSP is too strict for our app." -> Start with report-only mode and tighten iteratively.
- "innerHTML is fine for speed." -> It is a common XSS source; use safe alternatives.
- "Security headers are edge-only." -> App and CDN layers must align.
Evidence Pack
- CSP report summary and remediation log
- Security test evidence for XSS payloads
- Header validation output in staging and prod
- Third-party script inventory with owners
Exit Criteria
- Frontend attack surface is materially reduced
- Security regressions are caught before release
