Nosql Injection on Cloudflare

Cloudflare Workers often act as lightweight API gateways or serverless functions that forward requests to backend services such as Cloudflare D1 (SQLite), KV, or external databases. If input is directly interpolated into these calls without validation or parameterization, NoSQL injection can occur. For example, when building query filters for D1 using string concatenation, an attacker can manipulate query logic to bypass authentication or extract unintended records.

Attack patterns specific to Cloudflare include:

• KV namespace poisoning via key injection: If a Worker key prefix is built from user-controlled input (e.g., userId), an attacker can supply a payload like {"$ne": ""} to enumerate or override keys, effectively bypassing tenant isolation.
• D1 SQL-like injection through crafted WHERE clauses: D1 supports SQLite; unsafe string concatenation in SQL fragments can be abused. A payload such as 1 OR 1=1 appended to an email filter can return all rows.
• Authorization bypass via role tampering: If roles are stored in KV or D1 and referenced by user input, an attacker can supply {"$gt": "0"} to escalate privileges when the query is built dynamically.
• Prototype pollution in JSON parsing within Workers: When deserializing user JSON to construct queries, nested properties like __proto__ or constructor can alter object behavior, leading to logic bypasses or unexpected runtime evaluation.

In Cloudflare environments, these patterns commonly appear in routes like /api/users/:id/profile where id is used directly in KV lookups or D1 queries without sanitization. Because Workers execute at the edge, improperly validated input can propagate across data sources quickly, amplifying exposure of sensitive tenant data.

Detecting NoSQL injection in Cloudflare requires analyzing how user input is used in KV key construction, D1 queries, and JSON parsing within Workers. Static review of code paths that concatenate input into queries is effective, but dynamic testing is essential to uncover runtime behavior. middleBrick scans unauthenticated attack surfaces and includes checks aligned with the OWASP API Top 10, which helps identify injection risks in API endpoints that interact with Cloudflare services.

To detect these issues with middleBrick:

• Submit the Worker’s public URL to the scanner using the CLI: middlebrick scan https://your-worker.example.com.
• The scan runs 12 security checks in parallel, including Input Validation and Property Authorization, which surface anomalies such as unchecked object keys or unsafe query building.
• Leverage the OpenAPI/Swagger analysis feature if your Worker exposes a spec; middleBrick resolves $ref definitions and cross-references them with runtime findings to highlight mismatched authorization assumptions.
• LLM/AI Security checks are unique to middleBrick and can identify prompt injection or system prompt leakage if your Worker hosts AI endpoints; while not directly tied to NoSQL injection, this demonstrates the scanner’s breadth in edge environments.

Findings include severity ratings and remediation guidance, enabling teams to prioritize fixes based on exploitability and data exposure.

Remediation focuses on strict input validation, avoiding string concatenation for queries, and leveraging Cloudflare’s native libraries. Always treat user input as untrusted and encode or filter it before using it in KV keys or D1 queries.

KV namespace safety: Validate and sanitize keys to ensure they conform to expected patterns. Use a whitelist approach for key segments instead of dynamic concatenation.

// Unsafe
const userKey = `${userId}`;
const value = await USER_KV.get(userKey);

// Safe: enforce alphanumeric tenant IDs
const tenantId = input.id.replace(/[^a-zA-Z0-9_-]/g, '');
const userKey = `tenant:${tenantId}:profile`;
const value = await USER_KV.get(userKey);

D1 query parameterization: Use prepared statements or parameterized queries to prevent injection. Avoid embedding variables directly into SQL strings.

// Unsafe
const email = req.body.email;
const query = `SELECT * FROM users WHERE email = '${email}'`;
await D1.prepare(query).run();

// Safe: use parameterized queries
const email = req.body.email;
const query = 'SELECT * FROM users WHERE email = ?';
await D1.prepare(query).bind(email).run();

Role-based access control (RBAC) enforcement: Do not rely on client-supplied role objects. Fetch roles from a trusted source and validate against a strict schema before using them in authorization decisions.

// Unsafe
const role = await ROLE_KV.get(`role:${input.roleKey}`);
if (role && role.priority > user.priority) { /* allow */ }

// Safe: validate against a known schema and sanitize input
const roleKey = `role:${input.roleKey.replace(/[^a-z0-9]/g, '')}`;
const role = await ROLE_KV.get(roleKey);
if (role) {
  const parsed = JSON.parse(role);
  if (parsed.priority !== undefined && Number.isInteger(parsed.priority)) {
    if (parsed.priority > user.priority) { /* allow */ }
  }
}

JSON parsing safeguards: When parsing user JSON to construct dynamic queries, avoid exposing internal prototypes. Use JSON.parse with a reviver or a safe parser to strip dangerous keys.

// Unsafe
const filters = JSON.parse(userInput);
const query = buildQuery(filters);

// Safe: reviver to remove dangerous keys
const safeReviver = (key, value) => {
  if (key === '__proto__' || key === 'constructor') return undefined;
  return value;
};
const filters = JSON.parse(userInput, safeReviver);
const query = buildQuery(filters);

By combining these practices, teams can significantly reduce the attack surface while still leveraging Cloudflare’s edge capabilities.