Broken Access Control in Chi with Jwt Tokens

Broken Access Control (BOLA/IDOR) in the Chi web framework often intersects with JWT token handling in ways that expose endpoints to unauthorized data access or modification. When JWTs are used for session management but access checks are incomplete, an attacker can manipulate token claims or make direct authenticated requests to access or modify other users' resources.

Chi routes typically enforce authentication at the router level using guards that inspect JWT payloads. If route handlers then use user-supplied identifiers (e.g., /users/{id}) without verifying that the requesting user owns that identifier, a BOLA vulnerability arises. For example, a JWT may contain a sub claim identifying the user, but if the handler does not compare sub with the requested resource ID, an attacker can increment IDs or guess valid ones to access other users' data.

JWTs may also carry roles or scopes, but if Chi middleware does not enforce scope-based checks on sensitive endpoints, privilege escalation can occur. A token issued for read-only access might be reused to perform write operations if the handler does not validate specific scopes or permissions encoded in the JWT. This is especially risky when tokens have long lifetimes or are not properly invalidated on logout, increasing the window for abuse.

In Chi, developers might rely on opaque tokens without validating signature algorithms, leading to algorithm confusion attacks where an unsigned token is accepted. If the application decodes JWTs without verifying the signature or the expected issuer, an attacker can forge tokens and bypass access controls entirely. MiddleBrick scans detect such weaknesses by testing unauthenticated and authenticated surfaces, identifying endpoints where JWT validation is missing or misapplied.

Real-world patterns include missing ownership checks in endpoints like GET /api/users/{userId} or insufficient scope validation in admin routes. These issues align with OWASP API Top 10 A01:2023 broken access control and map to compliance frameworks such as PCI-DSS and SOC2. Continuous monitoring via the Pro plan helps detect regressions, while the CLI allows you to integrate scans into development workflows.

Remediation focuses on strict validation of JWTs and enforcing ownership and scope checks within Chi route handlers. Always verify the token signature, issuer, and audience before trusting its claims. Use a robust JWT library and ensure algorithm restrictions are in place to prevent confusion attacks.

Example: Validating JWT and enforcing ownership in Chi

import Jwt from 'jsonwebtoken';
import { Request, Response, NextFunction } from '@h4/http';

const PUBLIC_KEY = `-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA...
-----END PUBLIC KEY-----`;

function verifyToken(token: string) {
  return Jwt.verify(token, PUBLIC_KEY, {
    algorithms: ['RS256'],
    issuer: 'https://auth.example.com',
    audience: 'chi-api',
  });
}

export const requireAuth = (req: Request, res: Response, next: NextFunction) => {
  const authHeader = req.headers.authorization;
  if (!authHeader?.startsWith('Bearer ')) {
    return res.status(401).json({ error: 'Unauthorized' });
  }
  const token = authHeader.split(' ')[1];
  try {
    const payload = verifyToken(token);
    req.context.user = payload; // Attach decoded payload to request context
    next();
  } catch (err) {
    return res.status(401).json({ error: 'Invalid token' });
  }
};

Example: Enforcing ownership and scope checks

import { Request, Response, NextFunction } from '@h4/http';

export const requireScope = (requiredScope: string) => {
  return (req: Request, res: Response, next: NextFunction) => {
    const userScopes = (req.context.user as any).scope || [];
    if (!userScopes.includes(requiredScope)) {
      return res.status(403).json({ error: 'Insufficient scope' });
    }
    next();
  };
};

export const requireOwnership = (resource: 'users') => {
  return (req: Request, res: Response, next: NextFunction) => {
    const userId = req.params.id;
    const requestingUserId = (req.context.user as any).sub;
    if (resource === 'users' && userId !== requestingUserId) {
      return res.status(403).json({ error: 'Forbidden: cannot access other users' data' });
    }
    next();
  };
};

// Usage in Chi router
import { router, get } from '@h4/router';
import { requireAuth, requireScope, requireOwnership } from './auth';

router.get('/api/users/:id', requireAuth, requireOwnership('users'), (req, res) => {
  // Safe to serve user data
  res.json({ id: req.params.id, name: 'John Doe' });
});

router.post('/api/admin', requireAuth, requireScope('admin:write'), (req, res) => {
  res.json({ message: 'Admin action performed' });
});

These examples ensure JWTs are properly verified, ownership is checked against the requesting user, and scopes are enforced. Combine this with middleware that validates token revocation lists and short expirations to reduce risk. The free tier of MiddleBrick can surface misconfigurations in JWT handling, while the Pro plan enables continuous monitoring of these controls across your API surface.