Integer Overflow in Feathersjs with Basic Auth

An integer overflow in a Feathersjs service becomes significantly more dangerous when combined with Basic Auth due to the interplay between authentication parsing, user identity binding, and arithmetic operations on untrusted input. Basic Auth credentials are typically extracted from the Authorization header and decoded in middleware before the request reaches the service layer. If the code that parses or uses the decoded payload (for example, a numeric user identifier or a quantity used in calculations) does not validate integer size, an attacker can supply values that wrap around the integer type, leading to negative numbers, zero, or very large values that bypass length or ownership checks.

Consider a Feathersjs application that uses Basic Auth and performs arithmetic based on decoded user data. An attacker may send a crafted Authorization header where a numeric claim (such as an account ID or a quantity) is encoded as an unexpectedly large integer. If Feathersjs application code adds or multiplies this value without range checks, an overflow may occur. For example, a 32-bit signed integer may wrap from 2147483647 to -2147483648, which can cause conditional checks like userId > 0 to evaluate incorrectly, potentially enabling horizontal privilege escalation (BOLA/IDOR) by letting one user act on another’s resources.

In the context of the 12 parallel security checks run by middleBrick, Integer Overflow falls under Input Validation and BOLA/IDOR concerns. The scanner tests unauthenticated endpoints and, when Basic Auth is present, also evaluates whether authentication parsing introduces unsafe arithmetic. A real-world pattern resembles CVE scenarios where integer wraparound leads to unauthorized record access or incorrect permission evaluation. Because Basic Auth transmits credentials in an encoded header, server-side code must treat decoded numeric fields as untrusted input and apply strict bounds and type checks before using them in calculations.

An example vulnerable Feathersjs service might decode Basic Auth and directly use numeric fields from the payload without validation:

// Vulnerable: uses decoded numeric value without bounds checking
app.service('orders').hooks({
  before: {
    create: [context => {
      const { quantity } = context.data;
      // No validation for integer overflow
      if (quantity * 2 < quantity) {
        throw new Error('Invalid quantity');
      }
      return context;
    }]
  }
});

An attacker sending a very large quantity could trigger a wrap-around, causing the condition to pass incorrectly and leading to unexpected behavior such as negative prices or inventory inconsistencies. Remediation requires validating integer ranges and using safe arithmetic or BigInt when large values are expected, ensuring that identity and permission checks remain reliable even under crafted input.

Remediation for Integer Overflow in Feathersjs with Basic Auth centers on validating and sanitizing numeric inputs derived from authentication data or request payloads, and avoiding unsafe arithmetic. Always validate integers against safe ranges, use libraries for safe arithmetic when necessary, and enforce strict type checks before using values in permissions or calculations.

Below are concrete code examples for secure Feathersjs services using Basic Auth. The first example shows safe parsing and validation of integer inputs after Basic Auth extraction:

// Secure: validate integer input and use safe checks
const isSafeInteger = (value) =>
  Number.isInteger(value) && value >= 0 && value <= 2147483647;

app.service('orders').hooks({
  before: {
    create: [context => {
      const { quantity } = context.data;
      if (!isSafeInteger(quantity)) {
        throw new Error('Invalid or unsafe quantity');
      }
      // Safe arithmetic with explicit bounds
      const doubled = Math.multiplySafe ? quantity * 2 : quantity + quantity;
      context.data.quantity = doubled;
      return context;
    }]
  }
});

The second example demonstrates how to integrate validation with Basic Auth extracted user identifiers, ensuring that user-supplied numeric identifiers are checked before being used in data access patterns:

// Secure: validate userId from Basic Auth before use
app.service('users').hooks({
  before: {
    get: [context => {
      const { userId } = context.params.query; // assume passed after auth
      const id = Number(userId);
      if (!Number.isInteger(id) || id <= 0) {
        throw new Error('Invalid user identifier');
      }
      // Ensure the authenticated user can only access their own data
      if (context.params.user.id !== id) {
        throw new Error('Unauthorized');
      }
      return context;
    }]
  }
});

When using the CLI (middlebrick scan <url>) or the GitHub Action to integrate API security checks into CI/CD, these patterns help ensure findings related to Integer Overflow and Authentication Bypass are minimized. For teams needing deeper visibility, the Pro plan provides continuous monitoring and can alert when risk scores degrade, while the MCP Server allows scanning APIs directly from AI coding assistants to catch unsafe arithmetic during development.

Finally, always treat decoded Basic Auth fields as untrusted input. Validate numeric fields rigorously, prefer 64-bit integers or BigInt for calculations that may exceed safe ranges, and enforce the principle of least privilege so that even if an overflow occurs, the blast radius is limited.