Introspection in schema validation in Apollo Server

Summary

We encourage all users of Apollo Server to read this advisory in its entirety to understand the impact. The _Resolution_ section contains details on patched versions.

### Impact

If `subscriptions: false` is passed to the `ApolloServer` constructor options, there is no impact. If implementors were not expecting validation rules to be enforced on the WebSocket subscriptions transport **and** are unconcerned about introspection being enabled on the WebSocket subscriptions transport (or were not expecting that), then this advisory is not applicable. If `introspection: true` is passed to the `ApolloServer` constructor options, the impact is limited to user-provided validation rules (i.e., using `validationRules`) since there would be no expectation that introspection was disabled.

The enforcement of user-provided validation rules on the HTTP transport is working as intended and is unaffected by this advisory. Similarly, disabling introspection on the HTTP transport is working as intended and is unaffected by this advisory.

> **Note:** Unless `subscriptions: false` is explicitly passed to the constructor parameters of `new ApolloServer({ ... })`, **subscriptions are enabled by default, whether or not there is a `Subscription` type present in the schema.** As an alternative to upgrading to a patched version, see the _Workarounds_ section below to disable subscriptions if it is not necessary.

In cases where `subscriptions: false` is **not** explicitly set, the subscription server **is impacted** since validation rules which are enforced on the main request pipeline within Apollo Server were not being passed to the `SubscriptionServer.create` invocation ([seen here, prior to the patch](https://github.com/apollographql/apollo-server/blob/7d6f23443e52a90deb74f152f34bb76eea78ee19/packages/apollo-server-core/src/ApolloServer.ts#L677-L726)).

The omitted validation rules for the subscription server include any `validationRules` passed by implementors to the `ApolloServer` constructor which were expected to be enforced on the subscriptions WebSocket endpoint. **Additionally**, because an internal [`NoIntrospection`](https://github.com/apollographql/apollo-server/blob/7d6f23443/packages/apollo-server-core/src/ApolloServer.ts#L77-L88) validation rule is used to disable introspection, it would have been possible to introspect a server on the WebSocket endpoint that the `SubscriptionServer` creates even though it was not possible on other transports (e.g. HTTP).

**The severity of risk depends on whether sensitive information is being stored in the schema itself.** The contents of schema descriptions, or secrets which might be revealed by the names of types or field names within those types, will determine the risk to individual implementors.

### Affected packages

The bug existed in `apollo-server-core` versions prior to version 2.14.2, however, this means all integration packages (e.g., `apollo-server-express`, etc.) prior to version 2.14.2 which depend on `apollo-server-core` for their subscriptions support are affected. This includes the `apollo-server` package that automatically provides an Express server.

Therefore, for officially published Apollo Server packages, the full list of affected packages includes: `apollo-server`, `apollo-server-azure-functions`, `apollo-server-cache-memcached`, `apollo-server-core`, `apollo-server-cloud-functions`, `apollo-server-cloudflare`, `apollo-server-express`, `apollo-server-fastify`, `apollo-server-hapi`, `apollo-server-koa`, `apollo-server-lambda`, and `apollo-server-micro`.

> Note: The full list included here doesn't fit into the box provided by the GitHub Security Advisories form.

### Resolution

The problem is resolved in Apollo Server versions 2.14.2 or higher. If upgrading is not an option, see _Workarounds_ below. When upgrading, ensure that the affected integration package (e.g., `apollo-server-express`) **and** the `apollo-server-core` package are both updated to the patched versions. (The version numbers should both be 2.14.2.)

### Workarounds

Upgrading to a patched version is the recommended solution. If upgrading is not an option, subscriptions can be disabled with `subscriptions: false` to resolve the impact. **Disabling subscriptions in this way will disable _all_ subscriptions support and the WebSocket transport**:

```js const server = new ApolloServer({ subscriptions: false, /* Other options, such as typeDefs, resolvers, schema, etc. */ }); ```

### For more information If you have any questions or comments about this advisory, please [open an issue](https://github.com/apollographql/apollo-server/issues/new) and the maintainers will try to assist.

### Credit and appreciation

Apollo fully believes in ethical disclosure of vulnerabilities by security researchers who notify us with details and provide us time to address and fix the issues before publicly disclosing.

Credit for this discovery goes to the team at [Bitwala](https://www.bitwala.com/), who reported the concern to us responsibly after discovering it during their own auditing.