Buffer Overflow in Strapi with Basic Auth

A buffer overflow in Strapi becomes more exploitable when Basic Authentication is used in an unauthenticated scan context. Because Strapi can be configured to accept Basic Auth headers on admin or API routes, an attacker who discovers the endpoint can send oversized credentials or malformed Authorization values. If the underlying Node.js or framework layer does not properly bound input length, the oversized header can overflow a stack or heap buffer, leading to arbitrary code execution or service disruption.

In a black-box scan, middleBrick tests unauthenticated attack surfaces and also checks authenticated surfaces when credentials are provided. When Basic Auth is enabled but not rigorously validated, patterns such as long Base64-encoded credentials or deeply nested header structures can trigger parsing bugs in HTTP servers or custom auth middleware. These patterns are included in the unchecked input validation checks, where oversized or malformed headers are flagged as potential injection or overflow indicators.

Additionally, when an OpenAPI spec is provided, middleBrick cross-references spec definitions with runtime findings. If the spec describes security schemes using type: http with scheme basic but does not document length constraints or validation, the scanner highlights the mismatch. Runtime probes that send abnormally long Basic Auth strings can expose crashes or unexpected behavior, mapped to relevant CVEs involving memory corruption in underlying libraries. The system also flags related checks such as Input Validation and Unsafe Consumption, because missing length checks on credentials often coincide with missing sanitization on request bodies.

Remediation focuses on strict input validation, rejecting malformed or oversized credentials, and avoiding unsafe concatenation when constructing authentication responses. Always enforce length limits on the Authorization header value and use safe parsing libraries instead of manual splitting.

Example of vulnerable Basic Auth handling in Strapi (before fix):

// Unsafe: no length validation on auth header
strapi.app.use(async (ctx, next) => {
  const auth = ctx.request.header.authorization || '';
  if (auth.startsWith('Basic ')) {
    const decoded = Buffer.from(auth.slice(6), 'base64').toString('utf-8');
    const [user, pass] = decoded.split(':');
    // Direct use of user/pass without validation
    ctx.state.user = { user, pass };
  }
  await next();
});

Example of secure Basic Auth handling in Strapi (after fix):

// Safe: enforce header length and validate format
const MAX_BASIC_AUTH_LENGTH = 2048;
strapi.app.use(async (ctx, next) => {
  const auth = ctx.request.header.authorization || '';
  if (auth.length > MAX_BASIC_AUTH_LENGTH) {
    ctx.status = 400;
    ctx.body = { error: 'Authorization header too long' };
    return;
  }
  if (auth.startsWith('Basic ')) {
    const payload = auth.slice(6);
    if (!/^[A-Za-z0-9+/=]+$/.test(payload)) {
      ctx.status = 400;
      ctx.body = { error: 'Invalid Basic Auth encoding' };
      return;
    }
    const decoded = Buffer.from(payload, 'base64').toString('utf-8');
    const parts = decoded.split(':');
    if (parts.length !== 2 || parts.some((p) => p.length === 0)) {
      ctx.status = 400;
      ctx.body = { error: 'Invalid credentials format' };
      return;
    }
    const [user, pass] = parts;
    if (user.length > 100 || pass.length > 100) { // reasonable bounds
      ctx.status = 400;
      ctx.body = { error: 'Credential length exceeds limit' };
      return;
    }
    ctx.state.user = { user, pass };
  }
  await next();
});

Additional measures include rejecting non-ASCII bytes in credentials, normalizing inputs before comparison, and ensuring that downstream consumers of ctx.state.user do not directly evaluate or log raw credential values. These steps reduce the likelihood of parsing ambiguities that could be leveraged in overflow or injection attacks.