security-and-hardening

# Hardening Patterns

Code patterns and decision aids for the `security-and-hardening` skill. The skill states each rule; this file shows one concrete implementation of it. Open the section you need when you reach that code — it is not meant to be read top to bottom.

Shared checklists (threat modeling, pre-commit checks, security headers, CORS, the package-manager matrix, install-script gate, and the OWASP quick-reference tables) live in `../../../references/security-checklist.md`.

## OWASP Top 10 Prevention Patterns

These are prevention patterns, not a ranking. For the 2021 ordering, see the quick-reference table in `../../../references/security-checklist.md#owasp-top-10-quick-reference`.

### Injection

```typescript
// BAD: SQL injection via string concatenation
const query = `SELECT * FROM users WHERE id = '${userId}'`;

// GOOD: Parameterized query
const user = await db.query('SELECT * FROM users WHERE id = $1', [userId]);

// GOOD: ORM with parameterized input
const user = await prisma.user.findUnique({ where: { id: userId } });
```

### Broken Authentication

```typescript
// Password hashing
import { hash, compare } from 'bcrypt';

const SALT_ROUNDS = 12;
const hashedPassword = await hash(plaintext, SALT_ROUNDS);
const isValid = await compare(plaintext, hashedPassword);

// Session management
app.use(session({
  secret: process.env.SESSION_SECRET,  // From environment, not code
  resave: false,
  saveUninitialized: false,
  cookie: {
    httpOnly: true,     // Not accessible via JavaScript
    secure: true,       // HTTPS only
    sameSite: 'lax',    // CSRF protection
    maxAge: 24 * 60 * 60 * 1000,  // 24 hours
  },
}));
```

### Cross-Site Scripting (XSS)

```typescript
// BAD: Rendering user input as HTML
element.innerHTML = userInput;

// GOOD: Use framework auto-escaping (React does this by default)
return <div>{userInput}</div>;

// If you MUST render HTML, sanitize first
import DOMPurify from 'dompurify';
const clean = DOMPurify.sanitize(userInput);
```

### Broken Access Control

```typescript
// Always check authorization, not just authentication
app.patch('/api/tasks/:id', authenticate, async (req, res) => {
  const task = await taskService.findById(req.params.id);

  // Check that the authenticated user owns this resource
  if (task.ownerId !== req.user.id) {
    return res.status(403).json({
      error: { code: 'FORBIDDEN', message: 'Not authorized to modify this task' }
    });
  }

  // Proceed with update
  const updated = await taskService.update(req.params.id, req.body);
  return res.json(updated);
});
```

### Security Misconfiguration

```typescript
// Security headers (use helmet for Express)
import helmet from 'helmet';
app.use(helmet());

// Content Security Policy
app.use(helmet.contentSecurityPolicy({
  directives: {
    defaultSrc: ["'self'"],
    scriptSrc: ["'self'"],
    styleSrc: ["'self'", "'unsafe-inline'"],  // Tighten if possible
    imgSrc: ["'self'", 'data:', 'https:'],
    connectSrc: ["'self'"],
  },
}));

// CORS — restrict to known origins
app.use(cors({
  origin: process.env.ALLOWED_ORIGINS?.split(',') || 'http://localhost:3000',
  credentials: true,
}));
```

### Sensitive Data Exposure

```typescript
// Never return sensitive fields in API responses
function sanitizeUser(user: UserRecord): PublicUser {
  const { passwordHash, resetToken, ...publicFields } = user;
  return publicFields;
}

// Use environment variables for secrets
const API_KEY = process.env.STRIPE_API_KEY;
if (!API_KEY) throw new Error('STRIPE_API_KEY not configured');
```

### Server-Side Request Forgery (SSRF)

Any time the server fetches a URL the user influenced — webhooks, "import from URL", image proxies, link previews — an attacker can aim it at internal services (cloud metadata, `localhost`, private IPs).

```typescript
// BAD: fetch whatever the user gives you
await fetch(req.body.webhookUrl);

// GOOD: allowlist scheme + host, reject if ANY resolved IP is private, forbid redirects
import { lookup } from 'node:dns/promises';
import ipaddr from 'ipaddr.js';

const ALLOWED_HOSTS = new Set(['hooks.example.com']);

async function assertSafeUrl(raw: string): Promise<URL> {
  const url = new URL(raw);
  if (url.protocol !== 'https:') throw new Error('https only');
  if (!ALLOWED_HOSTS.has(url.hostname)) throw new Error('host not allowed');
  // Resolve ALL records; a single private/reserved address fails the check.
  const addrs = await lookup(url.hostname, { all: true });
  if (addrs.some((a) => ipaddr.parse(a.address).range() !== 'unicast')) {
    throw new Error('private/reserved IP');
  }
  return url;
}

await fetch(await assertSafeUrl(req.body.webhookUrl), { redirect: 'error' });
```

The `range() !== 'unicast'` check covers loopback, link-local `169.254.169.254` (cloud metadata, the #1 SSRF target), private, and unique-local ranges across IPv4 and IPv6.

**Caveat — this still has a TOCTOU gap.** `fetch` resolves DNS again after the check, so an attacker using a short-TTL record can rebind to an internal IP between validation and connection. For high-risk surfaces, resolve once and connect to the pinned IP, or put a filtering agent in front (`request-filtering-agent` / `ssrf-req-filter`).

## Input Validation Patterns

### Schema Validation at Boundaries

```typescript
import { z } from 'zod';

const CreateTaskSchema = z.object({
  title: z.string().max(200).trim().min(1),
  description: z.string().max(2000).optional(),
  priority: z.enum(['low', 'medium', 'high']).default('medium'),
  dueDate: z.string().datetime().optional(),
});

// Validate at the route handler
app.post('/api/tasks', async (req, res) => {
  const result = CreateTaskSchema.safeParse(req.body);
  if (!result.success) {
    return res.status(422).json({
      error: {
        code: 'VALIDATION_ERROR',
        message: 'Invalid input',
        details: result.error.flatten(),
      },
    });
  }
  // result.data is now typed and validated
  const task = await taskService.create(result.data);
  return res.status(201).json(task);
});
```

### File Upload Safety

```typescript
// Restrict file types and sizes
const ALLOWED_TYPES = ['image/jpeg', 'image/png', 'image/webp'];
const MAX_SIZE = 5 * 1024 * 1024; // 5MB

function validateUpload(file: UploadedFile) {
  if (!ALLOWED_TYPES.includes(file.mimetype)) {
    throw new ValidationError('File type not allowed');
  }
  if (file.size > MAX_SIZE) {
    throw new ValidationError('File too large (max 5MB)');
  }
  // Don't trust the file extension — check magic bytes if critical
}
```

### Destructive Operations on Derived Paths

A delete, move, or overwrite is only as safe as the value that names its target. Reading that value from the kernel, a job payload, or a sibling service proves where it *arrived from*, not who *wrote* it — another process's command line is as attacker-controlled as a form field. A shape check ("absolute path, at least one directory deep") proves well-formedness and gets mistaken for authorization; that is how a cleanup routine deletes the root instead of the leaf.

Before a destructive call, require all three: the resolved target sits under an **allowlisted root** (compare after resolving symlinks, never on the raw string); it is at least one level **below** that root, so a root is never itself the target; and it carries **evidence that it is yours**, read *before* the operation and before any teardown that removes it — otherwise "absent" and "not mine" are indistinguishable. On refusal, log the rejected target and stop: a cleanup that falls back to a broader default path is the failure this guards against. Worked example in `../../../references/security-checklist.md#destructive-path-operations`.

Two limits, because the check reads stronger than it is. A marker inside the tree is self-attestation — anything that can write there can write the marker — so the expected owner has to come from authenticated state, and the marker needs integrity protection (restrictive ownership, or a MAC) before it counts as authorization. And resolving a path and then operating on the *name* is a check/use race wherever an untrusted process can swap an ancestor: on a shared volume, hold the target by descriptor and use no-follow, beneath-the-root operations, or make sure the hierarchy cannot change for the duration.

## Dependency Audit Triage

Package-manager audits report known advisories; they do not prove a package is trustworthy or that vulnerable code is reachable. Use this decision tree:

```
The native package-manager audit reports a vulnerability
├── Severity: critical or high
│   ├── Is the vulnerable code reachable in runtime, build, test, or deployment paths?
│   │   ├── YES --> Fix immediately (update, patch, or replace the dependency)
│   │   └── NO (confirmed unused across those paths) --> Fix soon, but not a blocker
│   └── Is a fix available?
│       ├── YES --> Update to the patched version
│       └── NO --> Check for workarounds, consider replacing the dependency, or add to allowlist with a review date
├── Severity: moderate
│   ├── Reachable in production? --> Fix in the next release cycle
│   └── Dev-only? --> Fix when convenient, track in backlog
└── Severity: low
    └── Track and fix during regular dependency updates
```

**Key questions:**
- Is the vulnerable function actually called in your code path?
- Is the dependency a runtime dependency or dev-only?
- Is the vulnerability exploitable given your deployment context (e.g., a server-side vulnerability in a client-only app)?

When you defer a fix, document the reason and set a review date.

## Rate Limiting

```typescript
import rateLimit from 'express-rate-limit';

// General API rate limit
app.use('/api/', rateLimit({
  windowMs: 15 * 60 * 1000, // 15 minutes
  max: 100,                   // 100 requests per window
  standardHeaders: true,
  legacyHeaders: false,
}));

// Stricter limit for auth endpoints
app.use('/api/auth/', rateLimit({
  windowMs: 15 * 60 * 1000,
  max: 10,  // 10 attempts per 15 minutes
}));
```

**Count in a shared store once there is more than one process.** `express-rate-limit` keeps its counters in process memory by default. Behind a load balancer each instance holds its own count, so the effective limit is `max × instances`; on serverless or edge runtimes a fresh invocation starts from zero, so the auth limit above may never fire. Pass a shared `store` (Redis via `rate-limit-redis`), or use an HTTP-based limiter that works where a long-lived TCP connection does not (for example `@upstash/ratelimit`):

```typescript
import { Ratelimit } from '@upstash/ratelimit';
import { Redis } from '@upstash/redis';

const authLimiter = new Ratelimit({
  redis: Redis.fromEnv(),                       // UPSTASH_REDIS_REST_URL + _TOKEN
  limiter: Ratelimit.slidingWindow(10, '15 m'), // 10 attempts per 15 minutes, across all instances
});
const { success } = await authLimiter.limit(`login:${req.ip}`);
if (!success) return res.status(429).end();
```

## Secrets Management

```
.env files:
  ├── .env.example  → Committed (template with placeholder values)
  ├── .env          → NOT committed (contains real secrets)
  └── .env.local    → NOT committed (local overrides)

.gitignore must include:
  .env
  .env.local
  .env.*.local
  *.pem
  *.key
```

**Always check before committing:**
```bash
# Check for accidentally staged secrets
git diff --cached | grep -i "password\|secret\|api_key\|token"
```

**If a secret is ever committed, rotate it.** Deleting the line or rewriting history is not enough — assume it's compromised the moment it reaches a remote. Revoke and reissue the key first, then purge it from history.

## Data Classification

Classify personal data as you add fields, so export and deletion requests can find it later:

| Class | Examples | Handling |
|---|---|---|
| **Non-personal** | Aggregates, anonymized counts | Normal handling |
| **Personal (PII)** | Name, email, IP, device/user IDs | Minimize, access-control, include in export/delete |
| **Sensitive** | Health, finance, location, biometrics, gov IDs, anything about minors | Extra basis to collect, stricter access, often encryption + audit logging |

## LLM Output Handling

```typescript
// BAD: trusting model output as a command or as markup
const sql = await llm.generate(`Write SQL for: ${userQuestion}`);
await db.query(sql);                                   // arbitrary query execution
container.innerHTML = await llm.reply(userMessage);   // stored XSS, via the model

// GOOD: model output is data — parse defensively, then validate, then encode
let intent;
try {
  intent = CommandSchema.parse(JSON.parse(await llm.replyJson(userMessage)));
} catch {
  throw new ValidationError('unexpected model output'); // JSON.parse or schema failed
}
await runAllowlistedAction(intent.action, intent.params);
container.textContent = await llm.reply(userMessage);
```

---
name: security-and-hardening
description: Hardens code against vulnerabilities. Use when auditing an input handler for vulnerabilities, when handling user input, authentication, data storage, or external integrations, or when checking a login flow is safe against the OWASP Top Ten. Use when building any feature that accepts untrusted data, manages user sessions, or interacts with third-party services. Use when auditing dependencies for known vulnerabilities, triaging package-manager audit findings, or assessing supply-chain risk in a new package. Use when personal data or privacy compliance (GDPR, CCPA) is involved.
---

# Security and Hardening

## Overview

Security-first development practices for web applications. Treat every external input as hostile, every secret as sacred, and every authorization check as mandatory. Security isn't a phase — it's a constraint on every line of code that touches user data, authentication, or external systems.

## When to Use

- Building anything that accepts user input
- Implementing authentication or authorization
- Storing or transmitting sensitive data
- Integrating with external APIs or services
- Adding file uploads, webhooks, or callbacks
- Handling payment or PII data

## Process: Threat Model First

Controls bolted on without a threat model are guesses. Before hardening, spend five minutes thinking like an attacker:

1. **Map the trust boundaries.** Where does untrusted data cross into your system? HTTP requests, form fields, file uploads, webhooks, third-party APIs, message queues, and **LLM output** — plus the local values that look internal because the OS handed them to you: another process's command line or environment, filenames on a shared volume, a path in a job payload. Trust follows who *wrote* a value, not which channel delivered it. Every boundary is attack surface.
2. **Name the assets.** What's worth stealing or breaking? Credentials, PII, payment data, admin actions, money movement.
3. **Run STRIDE over each boundary** — a quick lens, not a ceremony:

| Threat | Ask | Typical mitigation |
|---|---|---|
| **S**poofing | Can someone impersonate a user/service? | Authentication, signature verification |
| **T**ampering | Can data be altered in transit or at rest? | Integrity checks, parameterized queries, HTTPS |
| **R**epudiation | Can an action be denied later? | Audit logging of security events |
| **I**nformation disclosure | Can data leak? | Encryption, field allowlists, generic errors |
| **D**enial of service | Can it be overwhelmed? | Rate limiting, input size caps, timeouts |
| **E**levation of privilege | Can a user gain rights they shouldn't? | Authorization checks, least privilege |

4. **Write abuse cases next to use cases.** For each feature, ask "how would I misuse this?" — then make that your first test.

If you can't name the trust boundaries for a feature, you're not ready to secure it. This is OWASP **A04: Insecure Design** — most breaches begin in design, not code.

## The Three-Tier Boundary System

### Always Do (No Exceptions)

- **Validate all external input** at the system boundary (API routes, form handlers)
- **Parameterize all database queries** — never concatenate user input into SQL
- **Encode output** to prevent XSS (use framework auto-escaping, don't bypass it)
- **Use HTTPS** for all external communication
- **Hash passwords** with bcrypt/scrypt/argon2 (never store plaintext)
- **Set security headers** (CSP, HSTS, X-Frame-Options, X-Content-Type-Options)
- **Use httpOnly, secure, sameSite cookies** for sessions
- **Run the detected package manager's native audit** against the committed lockfile before every release

### Ask First (Requires Human Approval)

- Adding new authentication flows or changing auth logic
- Storing new categories of sensitive data (PII, payment info)
- Adding new external service integrations
- Changing CORS configuration
- Adding file upload handlers
- Modifying rate limiting or throttling
- Granting elevated permissions or roles

### Never Do

- **Never commit secrets** to version control (API keys, passwords, tokens)
- **Never log sensitive data** (passwords, tokens, full credit card numbers)
- **Never trust client-side validation** as a security boundary
- **Never disable security headers** for convenience
- **Never use `eval()` or `innerHTML`** with user-provided data
- **Never store sessions in client-accessible storage** (localStorage for auth tokens)
- **Never expose stack traces** or internal error details to users

## Hardening Controls

The rules below are the workflow; a concrete implementation of each lives in [references/hardening-patterns.md](references/hardening-patterns.md). Open the section you need when you reach that code, not before.

### Injection, XSS, and access control

- Parameterize every query. Never build SQL, NoSQL, or shell commands from input strings.
- Encode output through the framework's auto-escaping. If raw HTML is unavoidable, sanitize with an allowlist sanitizer first.
- Check **authorization** on every request, not just authentication: the authenticated user must own, or be permitted on, the specific resource (A01, IDOR).

Patterns: [Injection](references/hardening-patterns.md#injection), [XSS](references/hardening-patterns.md#cross-site-scripting-xss), [Access control](references/hardening-patterns.md#broken-access-control).

### Authentication and sessions

- Hash passwords with bcrypt (≥12 rounds), scrypt, or argon2. The session secret comes from the environment, never from code.
- Session cookies are `httpOnly`, `secure`, and `sameSite: 'lax'` or `'strict'` (the CSRF defense; `'none'` sends the cookie on cross-site requests), with a bounded `maxAge`.

Pattern: [Authentication](references/hardening-patterns.md#broken-authentication).

### Headers, CORS, and responses

- Security headers on every response (helmet or the framework equivalent); CSP starts from `default-src 'self'` and is tightened, not loosened.
- CORS restricted to an explicit origin list from configuration. Never `*` with credentials.
- Strip sensitive fields (`passwordHash`, reset tokens) before any response. Error bodies are generic; internals go to server logs only.

Patterns: [Misconfiguration](references/hardening-patterns.md#security-misconfiguration), [Sensitive data exposure](references/hardening-patterns.md#sensitive-data-exposure).

### Input validation and uploads

- Validate at the boundary with a schema: allowlisted shape, lengths, enums, formats. Reject with 422 and structured details; downstream code uses only the parsed, typed value.
- Uploads: allowlist MIME types, cap size, verify content (magic bytes) when it matters. The extension proves nothing.

Patterns: [Schema validation](references/hardening-patterns.md#schema-validation-at-boundaries), [File upload](references/hardening-patterns.md#file-upload-safety).

### Server-side fetches (SSRF)

Any URL the user influences — webhooks, import-from-URL, image proxies, link previews — can be aimed at internal services. Allowlist scheme and host, resolve **all** DNS records and reject any private or reserved address (loopback, link-local `169.254.169.254`, private, unique-local, for IPv4 and IPv6), and forbid redirects. That check still has a DNS-rebinding TOCTOU gap: for high-risk surfaces, pin the resolved IP or put a filtering agent in front.

Pattern: [SSRF](references/hardening-patterns.md#server-side-request-forgery-ssrf).

### Destructive operations on derived paths

A delete, move, or overwrite is only as safe as the value naming its target, and trust follows who *wrote* that value, not which channel delivered it: another process's command line is as attacker-controlled as a form field. A shape check proves well-formedness, not authorization. Before the call, require all three: the resolved target (symlinks resolved) sits under an **allowlisted root**; it is at least one level **below** that root; and it carries **ownership evidence read before the operation**. On refusal, log the rejected target and stop; never fall back to a broader default path.

Why the check is weaker than it reads (marker self-attestation, check/use races): [Destructive paths](references/hardening-patterns.md#destructive-operations-on-derived-paths). Worked code: `../../references/security-checklist.md`.

### Rate limiting

Limit the API generally and auth endpoints strictly (about 10 attempts per 15 minutes). Once more than one process serves traffic, in-memory counters silently become `max × instances`, or never fire on serverless: back the limiter with a shared store.

Pattern: [Rate limiting](references/hardening-patterns.md#rate-limiting).

### Secrets

Secrets come from the environment. `.env.example` is committed with placeholders; real `.env*` files and key material are gitignored; grep the staged diff before committing. **A secret that reaches a remote is compromised the moment it lands: rotate it first, then purge history.**

Pattern: [Secrets management](references/hardening-patterns.md#secrets-management).

### Dependencies and supply chain

1. **Find the installation boundary and manager.** Use the workspace root that owns the lockfile, or an independent nested project only when it is outside that workspace. Corroborate `packageManager` (when present), the lockfile, and CI; stop on disagreement or competing lockfiles. Pin the manager version.
2. **Block dependency scripts before first execution.** Bootstrap with scripts disabled or a documented fail-closed policy, inspect the pending script source, approve only the minimum, commit the policy, then verify with a clean frozen/immutable install. Never blanket-approve.
3. **Run the native audit against the committed lockfile before every release.** Triage critical/high by **reachability** (runtime, build, test, deploy paths) and fix availability. Never apply forced remediation (`npm audit fix --force` or equivalent) automatically, since forced fixes may cross declared dependency ranges; preview, read changelogs, test each upgrade. Document every deferral with a reason and a review date.
4. **Audits only match known advisories.** They do not catch a newly malicious or typosquatted package (`cross-env` vs `crossenv`). Review new dependencies, lockfile diffs, and script-policy changes together: ownership, maintenance, release age, provenance, transitive graph. Verify registry signatures where supported (`npm audit signatures`, `pnpm audit signatures`) and treat their absence as a signal to investigate, not automatic proof of compromise (A06, LLM03).

Triage decision tree: [Dependency audit triage](references/hardening-patterns.md#dependency-audit-triage). Manager matrix and install-script gate: `../../references/security-checklist.md`.

### Personal data and privacy

Hardening asks "can an attacker read it?" Privacy asks "should *we* hold it at all, and for how long?" The cheapest data to protect, breach, and comply over is the data you never collected; treat personal data as a liability to minimize.

- **Classify fields as you add them** (non-personal, PII, sensitive) and handle each class accordingly. You cannot protect, or honor a deletion request for, data you cannot find.
- **Collect only against a stated purpose.** "Might be useful later" is latent breach scope, not a purpose. Keep PII out of telemetry (the `observability-and-instrumentation` skill makes the same point from the ops side).
- **Set retention up front, then actually delete.** Every personal-data store needs a TTL and a working deletion path, including backups, caches, search indexes, and analytics copies.
- **Support the data-subject rights your jurisdiction requires** (GDPR, CCPA, and kin): export, correct, delete. Design the schema so a user's data is findable and erasable, not smeared irreversibly across systems.
- **Consent gates collection and third-party sharing, and is auditable.** Sending PII to an analytics, ad, or LLM vendor is sharing; the vendor needs a data-processing agreement. Make region a configurable policy, not a hardcoded assumption.

Classification table: [Data classification](references/hardening-patterns.md#data-classification). A privacy incident starts the breach-notification clock; run the postmortem with the `debugging-and-error-recovery` skill.

### AI / LLM features

Calling an LLM — chatbots, summarizers, agents, RAG — adds a new attack surface; map it to the [OWASP Top 10 for LLM Applications (2025)](https://genai.owasp.org/llm-top-10/):

- **Model output is untrusted input** (LLM05). Never into `eval`, SQL, a shell, `innerHTML`, or a file path; parse defensively, validate against a schema, then encode.
- **Prompts can be hijacked** (LLM01). Untrusted text in the context — a user message, a fetched page, a PDF — can carry instructions. The system prompt is not a security boundary; enforce permissions in code.
- **Keep secrets, other tenants' data, and the full system prompt out of the context window** (LLM02, LLM07); scope tool permissions, validate every tool argument, and confirm destructive actions (LLM06); cap tokens, request rate, and recursion depth (LLM10); partition RAG embeddings per tenant and validate documents before indexing (LLM08).

Pattern: [LLM output handling](references/hardening-patterns.md#llm-output-handling).

## Review Checklist

Before sign-off, walk `../../references/security-checklist.md`: it covers authentication, authorization, input, data protection and privacy, headers and CORS, dependencies and supply chain, AI/LLM, and error handling, plus the OWASP quick-reference tables.

## Common Rationalizations

| Rationalization | Reality |
|---|---|
| "This is an internal tool, security doesn't matter" | Internal tools get compromised. Attackers target the weakest link. |
| "We'll add security later" | Security retrofitting is 10x harder than building it in. Add it now. |
| "No one would try to exploit this" | Automated scanners will find it. Security by obscurity is not security. |
| "The framework handles security" | Frameworks provide tools, not guarantees. You still need to use them correctly. |
| "It's just a prototype" | Prototypes become production. Security habits from day one. |
| "Threat modeling is overkill here" | Five minutes of "how would I attack this?" prevents the design flaws no control can patch later. |
| "It's just LLM output, it's only text" | That "text" can be a SQL statement, a script tag, or a shell command. Treat it like any untrusted input. |
| "The audit passed, so the dependency is safe" | Audits match known advisories. They do not detect a newly malicious package or make unreviewed install scripts safe to execute. |
| "Collect it now, we might need it later" | Data you don't hold can't be breached, subpoenaed, or mis-deleted. "Might need it" is breach scope, not a purpose. |
| "We'll handle deletion requests manually" | Manual erasure misses backups, caches, and analytics copies. If the schema can't find a user's data, you can't honor the request — design for it. |
| "Compliance is legal's problem, not ours" | Export, deletion, retention, and consent are schema and code. Legal can't bolt them on after you've smeared PII across ten systems. |

## Red Flags

- User input passed directly to database queries, shell commands, or HTML rendering
- A delete, move, or overwrite whose target comes from a payload, a config value, or another process's command line, guarded only by a shape check on the path
- Secrets in source code or commit history
- API endpoints without authentication or authorization checks
- Missing CORS configuration or wildcard (`*`) origins
- No rate limiting on authentication endpoints, or an in-memory limiter in front of more than one instance
- Stack traces or internal errors exposed to users
- Dependencies with known critical vulnerabilities, competing lockfiles at one installation boundary, non-reproducible installs, or blanket-approved scripts
- Server fetches user-supplied URLs without an allowlist (SSRF)
- LLM/model output passed into a query, the DOM, a shell, or `eval`
- Secrets, PII, or the full system prompt placed inside an LLM context window
- Personal data collected with no stated purpose, retention limit, or deletion path
- PII sent to analytics/ad/LLM vendors with no consent or data-processing agreement
- "Delete my account" that only flips a flag while the personal data lingers in stores and backups

## Verification

After implementing security-relevant code:

- [ ] The native audit has no unmitigated reachable critical/high findings; CI preserves the authoritative lockfile and blocks unreviewed dependency scripts
- [ ] No secrets in source code or git history
- [ ] All user input validated at system boundaries
- [ ] Destructive filesystem operations resolve symlinks, then verify allowlisted root, minimum depth, and ownership before running
- [ ] Authentication and authorization checked on every protected endpoint
- [ ] Security headers present in response (check with browser DevTools)
- [ ] Error responses don't expose internal details
- [ ] Rate limiting active on auth endpoints, backed by a shared store when more than one instance serves traffic
- [ ] Server-side URL fetches validated against an allowlist (no SSRF)
- [ ] LLM/model output validated and encoded before use (if AI features present)
- [ ] Personal data is classified, minimized to a stated purpose, and has a retention limit
- [ ] Deletion and export requests work end-to-end (including backups, caches, and analytics copies)