Frontend Security

---
name: frontend-security
description: Audit frontend codebases for security vulnerabilities and bad practices. Use when performing security reviews, auditing code for XSS/CSRF/DOM vulnerabilities, checking Content Security Policy configurations, validating input handling, reviewing file upload security, or examining Node.js/NPM dependencies. Target frameworks include web platform (vanilla HTML/CSS/JS), React, Astro, Twig templates, Node.js, and Bun. Based on OWASP security guidelines.
---

# Frontend Security Audit Skill

Perform comprehensive security audits of frontend codebases to identify vulnerabilities, bad practices, and missing protections.

## Audit Process

1. **Scan for dangerous patterns** - Search codebase for known vulnerability indicators
2. **Review framework-specific risks** - Check for framework security bypass patterns
3. **Validate defensive measures** - Verify CSP, CSRF tokens, input validation
4. **Check dependencies** - Review npm/node dependencies for vulnerabilities
5. **Report findings** - Categorize by severity with remediation guidance

## Critical Vulnerability Patterns to Search

### XSS Indicators (Search Priority: HIGH)

```bash
# React dangerous patterns
grep -rn "dangerouslySetInnerHTML" --include="*.jsx" --include="*.tsx" --include="*.js"

# Direct DOM manipulation
grep -rn "\.innerHTML\s*=" --include="*.js" --include="*.ts" --include="*.jsx" --include="*.tsx"
grep -rn "\.outerHTML\s*=" --include="*.js" --include="*.ts"
grep -rn "document\.write" --include="*.js" --include="*.ts"

# URL-based injection
grep -rn "location\.href\s*=" --include="*.js" --include="*.ts"
grep -rn "location\.replace" --include="*.js" --include="*.ts"
grep -rn "window\.open" --include="*.js" --include="*.ts"

# Eval and code execution
grep -rn "eval\s*(" --include="*.js" --include="*.ts"
grep -rn "new Function\s*(" --include="*.js" --include="*.ts"
grep -rn "setTimeout\s*(\s*['\"]" --include="*.js" --include="*.ts"
grep -rn "setInterval\s*(\s*['\"]" --include="*.js" --include="*.ts"

# Twig unescaped output
grep -rn "|raw" --include="*.twig" --include="*.html.twig"
grep -rn "{% autoescape false %}" --include="*.twig"
```

### CSRF Indicators

```bash
# Forms without CSRF tokens
grep -rn "<form" --include="*.html" --include="*.jsx" --include="*.tsx" --include="*.twig"

# State-changing requests without protection
grep -rn "fetch\s*(" --include="*.js" --include="*.ts" | grep -E "(POST|PUT|DELETE|PATCH)"
grep -rn "axios\.(post|put|delete|patch)" --include="*.js" --include="*.ts"
```

### Sensitive Data Exposure

```bash
# localStorage/sessionStorage with sensitive data
grep -rn "localStorage\." --include="*.js" --include="*.ts"
grep -rn "sessionStorage\." --include="*.js" --include="*.ts"

# Hardcoded secrets
grep -rn "api[_-]?key\s*[:=]" --include="*.js" --include="*.ts" --include="*.env"
grep -rn "secret\s*[:=]" --include="*.js" --include="*.ts"
grep -rn "password\s*[:=]" --include="*.js" --include="*.ts"
```

## Reference Documentation

Load these references based on findings:

- **XSS vulnerabilities found**: See `references/xss-prevention.md`
- **CSRF concerns**: See `references/csrf-protection.md`
- **DOM manipulation issues**: See `references/dom-security.md`
- **CSP review needed**: See `references/csp-configuration.md`
- **Input handling issues**: See `references/input-validation.md`
- **Node.js/NPM audit**: See `references/nodejs-npm-security.md`
- **Framework-specific patterns**: See `references/framework-patterns.md`
- **File upload handling**: See `references/file-upload-security.md`
- **JWT implementation**: See `references/jwt-security.md`

## Severity Classification

**CRITICAL** - Exploitable XSS, authentication bypass, secrets exposure
**HIGH** - Missing CSRF protection, unsafe DOM manipulation, SQL injection vectors
**MEDIUM** - Weak CSP, missing security headers, improper input validation
**LOW** - Informational disclosure, deprecated functions, suboptimal practices

## Report Format

```markdown
## Security Audit Report

### Summary
- Critical: X findings
- High: X findings
- Medium: X findings
- Low: X findings

### Critical Findings

#### [CRITICAL-001] Title
- **Location**: file:line
- **Pattern**: Code snippet
- **Risk**: Description of the vulnerability
- **Remediation**: How to fix
- **Reference**: OWASP link

### High Findings
[...]
```

## OWASP Reference Links

For comprehensive guidance, consult these OWASP cheatsheets directly:

- XSS Prevention: https://cheatsheetseries.owasp.org/cheatsheets/Cross_Site_Scripting_Prevention_Cheat_Sheet.html
- DOM XSS Prevention: https://cheatsheetseries.owasp.org/cheatsheets/DOM_based_XSS_Prevention_Cheat_Sheet.html
- CSRF Prevention: https://cheatsheetseries.owasp.org/cheatsheets/Cross-Site_Request_Forgery_Prevention_Cheat_Sheet.html
- CSP: https://cheatsheetseries.owasp.org/cheatsheets/Content_Security_Policy_Cheat_Sheet.html
- Input Validation: https://cheatsheetseries.owasp.org/cheatsheets/Input_Validation_Cheat_Sheet.html
- HTML5 Security: https://cheatsheetseries.owasp.org/cheatsheets/HTML5_Security_Cheat_Sheet.html
- DOM Clobbering: https://cheatsheetseries.owasp.org/cheatsheets/DOM_Clobbering_Prevention_Cheat_Sheet.html
- Node.js Security: https://cheatsheetseries.owasp.org/cheatsheets/Nodejs_Security_Cheat_Sheet.html
- NPM Security: https://cheatsheetseries.owasp.org/cheatsheets/NPM_Security_Cheat_Sheet.html
- AJAX Security: https://cheatsheetseries.owasp.org/cheatsheets/AJAX_Security_Cheat_Sheet.html
- File Upload: https://cheatsheetseries.owasp.org/cheatsheets/File_Upload_Cheat_Sheet.html
- Error Handling: https://cheatsheetseries.owasp.org/cheatsheets/Error_Handling_Cheat_Sheet.html
- JWT Security: https://cheatsheetseries.owasp.org/cheatsheets/JSON_Web_Token_for_Java_Cheat_Sheet.html
- User Privacy: https://cheatsheetseries.owasp.org/cheatsheets/User_Privacy_Protection_Cheat_Sheet.html
- gRPC Security: https://cheatsheetseries.owasp.org/cheatsheets/gRPC_Security_Cheat_Sheet.html