OpenNext Cloudflare: Cache interception can bypass middleware protection for encoded paths

Summary

When cache interception is enabled, @opennextjs/cloudflare can interpret percent-encoded paths differently during middleware matching and cache lookup.

An encoded request may fail to match authorization middleware, then be decoded into the cache key of a protected route. The cached response may consequently be returned without invoking the middleware.

enableCacheInterception is disabled by default.

Impact

A remote unauthenticated attacker may retrieve cached content from routes intended to be protected by middleware.

An application is affected when it:

• explicitly enables enableCacheInterception;
• relies on middleware for access control; and
• has a matching cached route.

Details

Middleware matching previously used the encoded request pathname, while cache interception decoded the pathname before selecting a cache entry.

For example, consider an application with:

• middleware matcher /admin/:path*;
• middleware returning 401 Authentication required for /admin;
• a statically generated, cached /admin route; and
• cache interception enabled:

export default defineCloudflareConfig({
  incrementalCache: staticAssetsIncrementalCache,
  enableCacheInterception: true,
});

An attacker can request:

GET /%61dmin

The encoded pathname does not match /admin/:path*, so the authorization middleware is not invoked. Cache interception then decodes %61dmin to admin and may return the cached /admin response:

HTTP/1.1 200 OK
x-opennext-cache: HIT

Protected content

Malformed paths exposed an additional inconsistency. For example:

GET /%61dmin/%ZZ

The previous implementation decoded each segment independently. It decoded %61dmin to admin but retained the malformed %ZZ segment, allowing cache lookup to continue using a partially decoded pathname.

Patches

The fix aligns encoded-path handling across middleware matching and cache lookup, and rejects malformed paths instead of partially decoding them. See the upstream fixes in opennextjs-aws#1199 and opennextjs-aws#1200.

Users should upgrade to @opennextjs/[email protected] or later.

Workarounds

If upgrading is not immediately possible for an application:

1. Disable cache interception by removing enableCacheInterception: true.
2. Enforce authorization inside protected route handlers rather than relying exclusively on middleware.
3. Reject encoded paths for protected routes at a trusted proxy before they reach the Worker.

Adding individual encoded matcher variants is not a complete workaround because pathnames can have multiple equivalent encodings.