Rate Limiting Bypass in Chi with Jwt Tokens

Chi is a lightweight HTTP framework for Node.js. When route-level rate limiting is implemented using JWT tokens without careful design, it can create bypass conditions that undermine intended request throttling. A typical pattern uses a middleware that reads a JWT payload to identify a user or API key and then applies limits per subject. For example, a developer might use a static in-memory store keyed by a claim such as sub or api_key and enforce a fixed number of requests per minute.

However, this approach can expose a Rate Limiting Bypass when the JWT is long-lived or when the rate limit is applied only at the middleware level before authorization checks. An attacker who obtains a valid JWT (for instance, through insecure storage, leakage in logs, or a weak issuance process) can reuse that token until the limit is exhausted. Additionally, if the implementation does not bind the rate limit to the token’s identity in a deterministic and server-side verifiable way, different tokens representing the same logical actor can bypass aggregate limits. This often occurs when the token is self-contained and the server does not maintain revocation or usage state, allowing rotation or replay of tokens to reset the effective count.

Another bypass vector arises from how Chi routes are structured. If rate limiting is applied to a broad path prefix and the JWT is validated on more specific routes, an attacker might use unauthenticated endpoints or public routes to consume quota without a valid token. Conversely, if the limit is enforced but not tied to the token’s scope (e.g., tenant or plan), a token with elevated scopes might be used to access multiple logical partitions and exhaust limits across them. The risk is compounded when responses do not consistently communicate rate limit status via headers, making it harder for clients to respect limits and easier for attackers to probe boundaries without detection.

Because middleBrick scans endpoints in black-box mode, it can detect inconsistencies such as missing rate limit enforcement on authenticated routes, inconsistent header disclosures, and patterns that suggest token-based limits can be evaded through token rotation or scope manipulation. These findings are surfaced alongside other checks, including Authentication and BOLA/IDOR, to highlight how weaknesses in identity handling can indirectly weaken rate limiting.

To mitigate Rate Limiting Bypass when using JWT tokens in Chi, tie rate limiting to a server-side verifiable subject and enforce limits consistently across authenticated routes. Use a stable identifier extracted from the validated token, such as the sub claim, and apply a sliding window or fixed window algorithm with a shared store to prevent token-based circumvention. Avoid relying solely on in-memory storage in clustered or serverless environments; prefer an external store that all instances can access.

Below is an example of a Chi middleware in TypeScript that integrates rate limiting with JWT validation using a consistent identifier and a simple in-memory map for demonstration. In production, replace the map with a distributed store such as Redis to ensure correctness across instances.

import { middleware, type MiddlewareHandler } from 'chii';
import { decode } from 'jose';

const RATE_LIMIT_WINDOW_MS = 60_000;
const MAX_REQUESTS = 100;
const requestCounts: Map = new Map();

const jwtRateLimit: MiddlewareHandler = async (ctx, next) => {
  const auth = ctx.req.header('authorization');
  if (!auth || !auth.startsWith('Bearer ')) {
    ctx.res = new Response('Unauthorized', { status: 401 });
    return;
  }

  const token = auth.slice(7);
  let decoded: { sub?: string; exp?: number };
  try {
    decoded = decode(token) as { sub?: string; exp?: number };
  } catch {
    ctx.res = new Response('Unauthorized', { status: 401 });
    return;
  }

  if (!decoded.sub) {
    ctx.res = new Response('Unauthorized', { status: 401 });
    return;
  }

  const now = Date.now();
  const key = decoded.sub;
  const record = requestCounts.get(key);

  if (!record) {
    requestCounts.set(key, { count: 1, resetAt: now + RATE_LIMIT_WINDOW_MS });
  } else if (now >= record.resetAt) {
    record.count = 1;
    record.resetAt = now + RATE_LIMIT_WINDOW_MS;
  } else {
    record.count += 1;
  }

  if (record.count > MAX_REQUESTS) {
    ctx.res = new Response('Too Many Requests', { status: 429 });
    return;
  }

  ctx.res = new Response(null as any, { status: 200 });
  await next();
};

export default middleware(jwtRateLimit);

For stronger security, validate the JWT signature against a known key or JWKS, verify issuer and audience claims, and enforce rate limits on a per-tenant basis when multi-tenancy is present. Ensure rate limit headers (e.g., X-RateLimit-Limit, X-RateLimit-Remaining, Retry-After) are included in responses so clients can adapt. Combine this with broader protections such as token binding, short token lifetimes, and secure storage practices to reduce the attack surface for token-related bypasses.