Heap Overflow in Feathersjs with Hmac Signatures

A heap-based buffer overflow in a Feathersjs service that uses Hmac Signatures can occur when unchecked input is used to size or copy memory on the server-side, often while processing Hmac signatures or related payloads. Although Feathersjs is a higher-level framework, vulnerabilities arise at the native or dependency layer (for example, within cryptographic libraries or C++ addons) and can be triggered through the request pipeline when signature verification consumes attacker-controlled data.

Consider a Feathersjs service that accepts a payload and an Hmac signature, then recomputes the signature for verification. If the implementation copies or parses input buffers into fixed-size stack or heap buffers without proper length checks, an oversized payload can corrupt adjacent memory. This can lead to arbitrary code execution, service crashes, or information disclosure during signature verification routines. Even though Feathersjs itself is JavaScript, the underlying Node.js runtime and native dependencies may expose heap-based weaknesses when handling malformed or specially crafted inputs.

Input validation and size checks must be applied before buffers are used in cryptographic operations. For example, an attacker may send an extremely large JSON body or header value that causes the Hmac verification code to allocate or copy data beyond expected boundaries. In an OpenAPI/Swagger context, if the API spec does not enforce strict size or type constraints for the payload and signature fields, the unauthenticated attack surface includes these endpoints for black-box scanning by middleBrick across its 12 checks, including Input Validation and Unsafe Consumption.

An insecure implementation might look like this:

const crypto = require('crypto');
const app = require('feathers')();
app.use('/sign', {
  async create(data, params) {
    const { payload, receivedSig } = data;
    const key = Buffer.from('secret-key');
    const computed = crypto.createHmac('sha256', key).update(payload).digest('hex');
    if (computed === receivedSig) {
      return { status: 'ok' };
    }
    throw new Error('Invalid signature');
  }
});

If payload is not bounded, an attacker can submit a very large string, causing high memory usage or a heap overflow inside Node.js or native crypto bindings during the update call. middleBrick’s checks for Property Authorization and Input Validation would surface missing constraints on payload size and signature format, while LLM/AI Security probes ensure that such endpoints are not exposing system prompts or leaking data through error messages during verification.

Because middleBrick scans unauthenticated attack surfaces and maps findings to frameworks like OWASP API Top 10 and GDPR, it highlights risky patterns in Hmac-based flows and provides remediation guidance without claiming to fix or block execution. Continuous monitoring in the Pro plan can track such regressions across API changes.

To mitigate heap overflow risks in Feathersjs services using Hmac Signatures, enforce strict input validation, limit payload sizes, and use constant-time comparison for signatures. Avoid passing unbounded user data directly into cryptographic update calls, and ensure buffers are sized appropriately before use.

Here is a hardened example:

const crypto = require('crypto');
const app = require('feathers')();

// Enforce max payload size (e.g., 1MB) to reduce heap pressure
const MAX_PAYLOAD_SIZE = 1024 * 1024;

app.use('/sign', {
  async create(data, params) {
    const { payload, receivedSig } = data;

    // Validate presence and types
    if (typeof payload !== 'string' || typeof receivedSig !== 'string') {
      throw new Error('Invalid input types');
    }

    // Limit payload size to prevent excessive heap allocation
    if (Buffer.byteLength(payload) > MAX_PAYLOAD_SIZE) {
      throw new Error('Payload too large');
    }

    const key = Buffer.from('secret-key');
    const computed = crypto.createHmac('sha256', key).update(payload, 'utf8').digest('hex');

    // Constant-time comparison to avoid timing leaks
    const isValid = crypto.timingSafeEqual(
      Buffer.from(computed),
      Buffer.from(receivedSig)
    );

    if (!isValid) {
      throw new Error('Invalid signature');
    }

    return { status: 'ok' };
  }
});

In this version, payload size is explicitly bounded before being fed into crypto.update, reducing the risk of heap exhaustion. Using Buffer.byteLength ensures accurate byte-size checks for UTF-8 strings. The comparison uses crypto.timingSafeEqual to prevent timing side-channels that could otherwise leak information about the expected signature.

For API contract safety, define an OpenAPI 3.0 schema that constrains the payload and signature fields:

paths:
  /sign:
    post:
      requestBody:
        content:
          application/json:
            schema:
              type: object
              required: [payload, receivedSig]
              properties:
                payload:
                  type: string
                  maxLength: 1048576
                receivedSig:
                  type: string
                  pattern: '^[a-f0-9]{64}$'

With the GitHub Action, you can enforce a minimum security score and fail builds if input validation or signature handling issues are detected. The CLI allows on-demand scans from the terminal, and the MCP Server enables scanning directly from AI coding assistants to catch such issues early in development.