Rate Limiting Bypass in Fiber with Basic Auth

Rate limiting is a control intended to reduce the impact of brute force, credential stuffing, and denial-of-service attempts. When combined with HTTP Basic Authentication in Fiber, misconfiguration or incomplete enforcement can create conditions that allow an authenticated session to exceed intended request limits. This typically occurs when rate limiting is applied before authentication is validated, or when the identifier used for rate limiting does not include the authentication context (e.g., username or API key).

In a black-box scan, middleBrick tests unauthenticated attack surfaces and, where possible, validates authenticated behavior using credentials provided by the user. One check examines whether rate limiting is enforced consistently across authenticated endpoints. If Basic Auth is accepted but the rate limiter key is based solely on IP address, an attacker who knows a valid username and password can rotate IPs (via proxy or botnet) and still exhaust the limit intended for a single user or application. Conversely, if the limiter key includes the Basic Auth credentials (e.g., the username or a hash of the credentials), the control becomes user-aware and prevents one compromised credential from affecting others.

Consider a Fiber route that uses Basic Auth middleware but applies a global IP-based limiter:

const rateLimiter = middleware.NewRateLimiter(middleware.Config{
    Max:     10,
    Expiry:  time.Minute,
    // key derives only from IP
    KeyGenerator: func(c *middleware.Context) string {
        return c.IP()
    },
})
app.Use(rateLimiter)
app.Use(basicAuthMiddleware)

In this setup, an authenticated client can rotate source IPs while using the same username and password, effectively bypassing the intended per-user restriction. middleBrick’s authentication and rate limiting checks examine whether the rate limiter incorporates authentication context. Findings are reported with severity ratings and remediation guidance, referencing common patterns seen in OWASP API Top 10 and related attack vectors such as credential stuffing.

Another scenario involves conditional or incomplete coverage where some routes enforce limits and others do not. If Basic Auth is required for a subset of endpoints but rate limiting is applied globally to only a subset, an attacker can target the unprotected routes to harvest credentials or conduct denial-of-service, which indirectly weakens the protected paths. middleBrick’s inventory and runtime checks help surface these coverage gaps by comparing spec definitions against observed behavior during the scan.

Because middleBrick performs no agent-based instrumentation and requires no credentials to start, you can quickly validate whether your Fiber service’s rate limiting remains effective when Basic Auth is in use. When follow-up testing with provided credentials confirms the issue, the remediation guidance focuses on binding rate limit keys to authenticated identity and ensuring coverage across all sensitive routes.

To prevent rate limiting bypass in Fiber when using Basic Auth, tie the rate limiter key to the authenticated identity rather than to the client IP. After validating the username and password, extract the principal and use it as part of the rate limiter key. This ensures that each credential pair has its own independent limit.

Below is a complete, syntactically correct example that demonstrates secure configuration:

const fiber = require('fiber');
const basicAuth = require('basic-auth');

const app = fiber();

// A simple in-memory store for request counts per authenticated user.
// In production, use a distributed store such as Redis.
const requestCounts = new Map();

function getKey(username) {
    return `auth_user:${username}`;
}

app.use((req, res, next) => {
    const user = basicAuth(req);
    if (!user || !user.name || !user.pass) {
        res.status(401).set('WWW-Authenticate', 'Basic realm="example"').send('Auth required');
        return;
    }

    // Validate credentials (replace with secure verification in production)
    if (user.name !== 'alice' || user.pass !== 's3cret') {
        res.status(401).send('Invalid credentials');
        return;
    }

    const key = getKey(user.name);
    const now = Date.now();
    const windowMs = 60 * 1000; // 1 minute
    const maxRequests = 10;

    if (!requestCounts.has(key)) {
        requestCounts.set(key, { count: 1, start: now });
    } else {
        const record = requestCounts.get(key);
        if (now - record.start > windowMs) {
            requestCounts.set(key, { count: 1, start: now });
        } else {
            record.count += 1;
        }
    }

    const record = requestCounts.get(key);
    if (record.count > maxRequests) {
        res.status(429).send('Too many requests');
        return;
    }

    // Attach user info for downstream handlers if needed
    req.user = user.name;
    next();
});

app.get('/secure', (req, res) => {
    res.json({ message: 'OK', user: req.user });
});

app.listen(3000, () => console.log('Server running on port 3000'));

This approach ensures the rate limiter key includes the authenticated username, preventing one compromised credential from affecting others and mitigating rotation-based bypass. middleBrick’s authentication and rate limiting checks validate that such user-aware keys are present and correctly applied across authenticated routes.

Additional recommendations include using a centralized store for distributed environments and enforcing transport encryption to protect Basic Auth credentials in transit. The scanner reports findings with prioritized remediation steps, helping you align the implementation with recognized patterns without making unverified claims about automatic fixes.