linktree-security-basics

Linktree Security Basics

Overview

Linktree integrations handle user-generated content (link titles, URLs, bios) and analytics data that is PII-adjacent — click counts, geographic breakdowns, and referrer URLs can fingerprint individual visitors. Bearer token authentication means a leaked key grants full account access including link creation, profile modification, and analytics export. Webhook payloads carry real-time event data signed with HMAC-SHA256, and failing to verify signatures opens your endpoint to spoofed events and data poisoning.

Prerequisites

• Secrets manager (AWS SSM, GCP Secret Manager, or Vault) for all Linktree credentials
• HTTPS enforced on all webhook receiver endpoints
• .env files in .gitignore — never committed to version control
• Logging infrastructure that supports field-level redaction

API Key Management

// Load Linktree bearer token from environment — never hardcode
const LINKTREE_TOKEN = process.env.LINKTREE_API_KEY;

function validateLinktreeConfig(): void {
  if (!LINKTREE_TOKEN || LINKTREE_TOKEN.startsWith('lt_test_')) {
    throw new Error('Missing or test-only LINKTREE_API_KEY — set a production token');
  }
}

function linktreeHeaders(): Record<string, string> {
  return {
    Authorization: `Bearer ${LINKTREE_TOKEN}`,
    'Content-Type': 'application/json',
  };
}
// Call validateLinktreeConfig() at startup, before accepting requests

Webhook Signature Verification

import crypto from 'node:crypto';

const WEBHOOK_SECRET = process.env.LINKTREE_WEBHOOK_SECRET!;

function verifyLinktreeWebhook(payload: string, signature: string): boolean {
  const expected = crypto
    .createHmac('sha256', WEBHOOK_SECRET)
    .update(payload, 'utf8')
    .digest('hex');
  // Timing-safe comparison prevents timing attacks
  return crypto.timingSafeEqual(Buffer.from(signature), Buffer.from(expected));
}

// Express middleware
app.post('/webhooks/linktree', (req, res) => {
  const sig = req.headers['x-linktree-signature'] as string;
  if (!sig || !verifyLinktreeWebhook(JSON.stringify(req.body), sig)) {
    return res.status(401).json({ error: 'Invalid signature' });
  }
  // Process verified event
});

Input Validation

import { URL } from 'node:url';

function sanitizeLinkTitle(title: string): string {
  // Strip HTML/script tags from user-generated link titles
  return title.replace(/<[^>]*>/g, '').trim().slice(0, 150);
}

function validateLinkUrl(url: string): boolean {
  try {
    const parsed = new URL(url);
    // Only allow http/https — block javascript:, data:, file: schemes
    return ['http:', 'https:'].includes(parsed.protocol);
  } catch {
    return false;
  }
}

Data Protection

function redactAnalytics(data: Record<string, unknown>): Record<string, unknown> {
  const sensitive = ['ip_address', 'user_agent', 'referrer_url', 'geo_city'];
  const redacted = { ...data };
  for (const field of sensitive) {
    if (redacted[field]) redacted[field] = '[REDACTED]';
  }
  return redacted;
}
// Use redactAnalytics() before writing any analytics payload to logs

Access Control

// Linktree tokens are account-scoped — enforce least privilege
function assertReadOnlyScope(operation: string): void {
  const writeOps = ['create_link', 'update_link', 'delete_link', 'update_profile'];
  if (writeOps.includes(operation) && process.env.LINKTREE_READ_ONLY === 'true') {
    throw new Error(`Write operation "${operation}" blocked in read-only mode`);
  }
}

Security Checklist

• Bearer token stored in secrets manager, not .env on disk
• Webhook x-linktree-signature verified with HMAC-SHA256
• Link URLs validated against allowlisted protocols
• Link titles sanitized for HTML/XSS before storage or display
• Analytics data redacted before logging (IP, user-agent, geo)
• Read-only mode enforced for non-admin integrations
• Token rotation scheduled quarterly
• Rate limiting applied to webhook receiver endpoint

Error Handling

Vulnerability	Risk	Mitigation
Bearer token in logs	Full account takeover	Redact Authorization header in all log output
Unverified webhooks	Spoofed link-click events	Reject any request missing valid x-linktree-signature
Malicious link URLs	Open redirect / phishing	Validate URL scheme and domain before storing
XSS in link titles	Script injection via UGC	Strip HTML tags and enforce max length
Analytics PII leakage	GDPR/CCPA violation	Redact IP, geo, and referrer before persistence

Resources

• Linktree Developer Docs
• OWASP API Security Top 10

Next Steps

See linktree-prod-checklist.