Unicode Normalization on Digitalocean

Digitalocean services such as App Platform, Functions, Spaces (object storage), and Managed Databases often accept user‑provided strings as part of API requests — for example, query parameters, header values, object keys, or JSON payloads. When these strings are used to make access‑control decisions (e.g., checking whether a user owns a specific Space object or whether a function is allowed to read a particular database table), differences in Unicode representation can lead to bypasses.

Consider a Space bucket named user‑data. An attacker could upload an object with the key useŕ-data (the letter ‘e’ followed by a combining acute accent) which, under NFC normalization, is visually identical to user‑data but byte‑wise different. If the application compares the raw key without normalizing, the check if key == "user-data" fails, allowing the attacker to create a hidden object that later appears as a legitimate file when the service normalizes keys for listing or serving.

Another common path is in Digitalocean App Platform route handling. A request to https://example.com/api/resórce (using the precomposed ‘ó’) might be routed differently than https://example.com/api/resórce (using ‘o’ + combining acute). If the router does not normalize the path before matching, an attacker could reach an unintended endpoint, potentially exposing internal APIs that lack authentication.

These issues fall under the OWASP API Security Top 10 category A1: Broken Object Level Authorization (BOLA/IDOR) and A3: Excessive Data Exposure, because the root cause is insufficient validation and normalization of user‑supplied Unicode data before it is used in security decisions.

middleBrick’s black‑box scanner includes input‑validation and property‑authorization checks that can surface Unicode‑normalization problems without needing source code or credentials. When you submit a Digitalocean‑hosted API URL, middleBrick:

• Sends a series of probes that vary the Unicode representation of parameters (NFC, NFD, NFKC, NFKD) while keeping the visual appearance constant.
• Monitors responses for changes in status code, returned data, or error messages that indicate the server treated the two variants differently.
• Flags findings under the "Input Validation" and "Property Authorization" categories, providing a severity rating and the exact payload that caused the divergence.

For example, if an endpoint /api/v1/resources/{id} returns 200 for id=resórce but 404 for id=resórce, middleBrick will report a "Unicode Normalization bypass" finding, noting that the identifier is used directly in a database lookup without prior normalization.

Because the scan is unauthenticated and takes only 5–15 seconds, you can quickly test staging or production Digitalocean APIs (App Platform services, Functions, or custom Droplets) and receive a prioritized list of Unicode‑related issues alongside the other 11 security checks.

The fix is to normalize all externally supplied Unicode strings to a single canonical form before they are used for access control, routing, or storage keys. Digitalocean’s supported runtimes (Node.js, Go, Python) provide built‑in or library‑based normalization functions.

Node.js (App Platform or Functions)

const { normalize } = require('unorm'); // npm i unorm

function handleRequest(req, res) {
  // Normalize query parameter "id" to NFC
  const rawId = req.query.id;
  const safeId = normalize('NFC', rawId);

  // Use safeId in downstream logic (e.g., DB lookup, Space key)
  const resource = db.getResource(safeId);
  if (!resource) return res.status(404).send('Not found');

  res.json(resource);
}

If you prefer not to add a dependency, the native String.prototype.normalize() method (available in Node ≥ 0.12) does the same:

const safeId = req.query.id.normalize('NFC');

Go (App Platform or Kubernetes)

package main

import (
	"golang.org/x/text/unicode/norm"
	"net/http"
)

func handler(w http.ResponseWriter, r *http.Request) {
	rawID := r.URL.Query().Get("id")
	// Normalize to NFC
	safeID := norm.NFC.String(rawID)

	// Proceed with safeID
	resource, err := lookupResource(safeID)
	if err != nil {
		http.Error(w, "not found", http.StatusNotFound)
		return
	}
	// ...
}

Python (App Platform or Functions)

import unicorn  # not needed; use built‑in unicorn module
import unicodedata

def handler(request):
    raw_id = request.args.get('id')
    # Normalize to NFC
    safe_id = unicodedata.normalize('NFC', raw_id)
    # Use safe_id
    resource = get_resource(safe_id)
    if not resource:
        return {'error': 'not found'}, 404
    return resource

When storing objects in Digitalocean Spaces, apply the same normalization to the key before calling the PUT operation:

const AWS = require('aws-sdk');
const spacesEndpoint = new AWS.Endpoint('nyc3.digitaloceanspaces.com');
const s3 = new AWS.S3({endpoint: spacesEndpoint});

const rawKey = userProvidedFilename;
const normKey = rawKey.normalize('NFC'); // Node.js

s3.putObject({
  Bucket: 'my-bucket',
  Key: normKey,
  Body: fileData,
  ACL: 'private'
}, (err, data) => {
  // …
});

By normalizing at the edge of trust — immediately after receiving user input — you eliminate the class of Unicode‑based bypasses while preserving compatibility with legitimate international characters.