Buffer Overflow in Sails with Basic Auth

A buffer overflow in a Sails.js application that uses HTTP Basic Authentication arises when unbounded or insufficiently validated data from the Authorization header is copied into fixed-size buffers on the stack. In C/C++ add-ons or native modules invoked during request handling, if the username or password extracted from the header is read with functions like strcpy or memcpy without length checks, an oversized credential can overflow the destination buffer. The unauthenticated attack surface that middleBrick scans means an attacker can probe the endpoint without credentials; the presence of Basic Auth does not hide the endpoint, and oversized headers can still trigger the overflow before any application logic evaluates the credentials.

The interaction with Basic Auth is notable because the credentials travel in an RFC 7617 header on every request, increasing exposure compared to optional bearer tokens. If the server parses the header naively in native code, the risk is not just data corruption but potential code execution. A crafted request with a long password or username can overwrite saved return addresses or exception handlers. Findings from middleBrick’s checks—such as Input Validation and Unsafe Consumption—highlight unsafe string handling and missing bounds enforcement. Even though middleBrick does not fix or block, it surfaces these patterns so developers can correlate runtime behavior with static analysis of the native components and the unauthenticated scan results that include header-processing paths.

Real-world patterns mirror known weaknesses like CVE-2019-11265 in related stacks where oversized headers led to memory corruption. The OWASP API Security Top 10 category ‘2: Broken Authentication’ intersects with ‘5: Injection’ when the overflow is leveraged to execute injected shellcode. Data Exposure and Encryption checks in the scan can indicate whether sensitive headers are logged in cleartext during the overflow-triggering request, compounding impact. The scanner’s active probing does not authenticate, so it evaluates how the service behaves under malformed credentials, emphasizing the need to validate and constrain all header inputs regardless of authentication mechanism.

Remediation focuses on eliminating unbounded copies and validating credential size before use. In Sails.js, keep credentials out of native add-ons or enforce strict length limits and use safe string routines when headers are processed in native code. Prefer framework-managed sessions or tokens over Basic Auth where feasible; if Basic Auth is required, ensure the server does not pass raw header strings directly to vulnerable functions.

Example safe handling in a Sails hook or controller (Node.js):

// Safe Basic Auth parsing in a Sails hook or controller
const AUTH_HEADER = 'authorization';
const MAX_CREDENTIAL_LENGTH = 256;

module.exports.parseBasicAuth = (req) => {
  const authHeader = req.headers[AUTH_HEADER];
  if (!authHeader || !authHeader.startsWith('Basic ')) {
    return null;
  }
  const encoded = authHeader.slice('Basic '.length).trim();
  // Limit header size before base64 decoding to mitigate resource abuse
  if (authHeader.length > MAX_CREDENTIAL_LENGTH) {
    throw new Error('Authorization header too large');
  }
  let credentials;
  try {
    credentials = Buffer.from(encoded, 'base64').toString('utf8');
  } catch (err) {
    throw new Error('Invalid base64 encoding');
  }
  const separatorIndex = credentials.indexOf(':');
  if (separatorIndex === -1) {
    throw new Error('Malformed credentials');
  }
  const username = credentials.slice(0, separatorIndex);
  const password = credentials.slice(separatorIndex + 1);
  // Enforce length limits on username and password
  if (username.length > MAX_CREDENTIAL_LENGTH || password.length > MAX_CREDENTIAL_LENGTH) {
    throw new Error('Username or password exceeds length limit');
  }
  // Further validation: allowlist characters if applicable
  if (!/^[a-zA-Z0-9._-]+$/.test(username)) {
    throw new Error('Invalid username format');
  }
  return { username, password };
};

// Usage in a Sails controller action
login: async function (req, res) {
  try {
    const creds = parseBasicAuth(req);
    if (!creds) {
      return res.unauthorized();
    }
    const user = await User.findOne({ username: creds.username });
    if (!user || user.password !== hash(creds.password)) {
      return res.unauthorized();
    }
    return res.ok({ token: generateSessionToken(user) });
  } catch (err) {
    return res.badRequest({ error: err.message });
  }
}

For native add-ons, validate lengths in C/C++ using strncpy or better yet use APIs that accept size and avoid overflows; ensure the buffer size is constant and reject inputs that exceed it. Combine these checks with the runtime observations that middleBrick reports—such as Input Validation and Data Exposure—to prioritize fixes where the scanner detects unsafe header handling in unauthenticated scans.