- name
- application-security
- description
- >-
Application Security Skill
Secure coding patterns, vulnerability prevention, and security tooling for web applications.
OWASP Top 10 (2021) with Code Examples
A01: Broken Access Control
// BAD - No authorization check
app.get('/api/users/:id', async (req, res) => {
const user = await db.user.findUnique({ where: { id: req.params.id } });
res.json(user);
});
// GOOD - Verify ownership or role
app.get('/api/users/:id', authenticate, async (req, res) => {
if (req.user.id !== req.params.id && req.user.role !== 'ADMIN') {
return res.status(403).json({ error: 'Forbidden' });
}
const user = await db.user.findUnique({ where: { id: req.params.id } });
res.json(user);
});A02: Cryptographic Failures
// BAD - Weak hashing
import crypto from 'crypto';
const hash = crypto.createHash('md5').update(password).digest('hex');
// GOOD - Use bcrypt with proper rounds
import bcrypt from 'bcrypt';
const hash = await bcrypt.hash(password, 12);
const isValid = await bcrypt.compare(password, hash);A03: Injection
// BAD - SQL injection
const query = `SELECT * FROM users WHERE email = '${email}'`;
// GOOD - Parameterized queries (Prisma handles this automatically)
const user = await prisma.user.findUnique({ where: { email } });
// GOOD - Parameterized raw SQL when needed
const users = await prisma.$queryRaw`SELECT * FROM users WHERE email = ${email}`;A07: Cross-Site Scripting (XSS)
// BAD - Rendering raw HTML
element.innerHTML = userInput;
// GOOD - Use textContent or framework escaping
element.textContent = userInput;
// GOOD - React auto-escapes by default
return <div>{userInput}</div>;
// BAD in React - dangerouslySetInnerHTML
return <div dangerouslySetInnerHTML={{ __html: userInput }} />;Content Security Policy (CSP)
Recommended Headers
// Next.js middleware
import { NextResponse } from 'next/server';
export function middleware(request: Request) {
const nonce = crypto.randomUUID();
const csp = [
`default-src 'self'`,
`script-src 'self' 'nonce-${nonce}'`,
`style-src 'self' 'unsafe-inline'`,
`img-src 'self' data: https:`,
`font-src 'self'`,
`connect-src 'self' https://api.example.com`,
`frame-ancestors 'none'`,
`base-uri 'self'`,
`form-action 'self'`,
].join('; ');
const response = NextResponse.next();
response.headers.set('Content-Security-Policy', csp);
response.headers.set('X-Content-Type-Options', 'nosniff');
response.headers.set('X-Frame-Options', 'DENY');
response.headers.set('Referrer-Policy', 'strict-origin-when-cross-origin');
response.headers.set('Permissions-Policy', 'camera=(), microphone=(), geolocation=()');
return response;
}SAST/DAST Tooling
Static Analysis (SAST)
| Tool | Language | Usage |
|---|---|---|
| ESLint security plugins | JS/TS | eslint-plugin-security, @microsoft/eslint-plugin-sdl |
| Semgrep | Multi | semgrep --config=auto . |
| Bandit | Python | bandit -r src/ |
| gosec | Go | gosec ./... |
| cargo-audit | Rust | cargo audit |
Dynamic Analysis (DAST)
| Tool | Purpose | Usage |
|---|---|---|
| OWASP ZAP | Web app scanning | Proxy-based scanner, API scan mode |
| Nuclei | Vulnerability scanning | Template-based scanner |
| Burp Suite | Manual + automated | Professional penetration testing |
Dependency Scanning
# Node.js
npm audit
npm audit fix
# Python
pip-audit
safety check
# Go
govulncheck ./...
# Rust
cargo auditInput Validation Patterns
Server-Side Validation (Always Required)
import { z } from 'zod';
const CreateUserSchema = z.object({
email: z.string().email().max(255),
name: z.string().min(1).max(100).regex(/^[a-zA-Z\s'-]+$/),
age: z.number().int().min(0).max(150).optional(),
});
function createUser(input: unknown) {
const validated = CreateUserSchema.parse(input);
// validated is now typed and safe
}Rate Limiting
import rateLimit from 'express-rate-limit';
const authLimiter = rateLimit({
windowMs: 15 * 60 * 1000, // 15 minutes
max: 5, // 5 attempts per window
message: 'Too many login attempts, please try again later',
standardHeaders: true,
legacyHeaders: false,
});
app.use('/api/auth/login', authLimiter);Security Checklist
- [ ] All user input validated server-side
- [ ] Parameterized queries for all database operations
- [ ] CSP headers configured
- [ ] Rate limiting on auth endpoints
- [ ] CORS properly restricted
- [ ] Secrets in environment variables, not code
- [ ] Dependencies scanned for vulnerabilities
- [ ] Authentication tokens in httpOnly cookies
- [ ] HTTPS enforced in production
- [ ] Error messages don't leak internal details
Related Resources
~/.claude/docs/reference/checklists/security-hardening.md- Security hardening checklist~/.claude/agents/security-auditor.md- Security audit agent~/.claude/skills/authentication-patterns/SKILL.md- Auth patterns
_Secure by default. Validate at boundaries. Defense in depth._