Cross-Site Request Forgery (CSRF) Prevention
Prevent CSRF attacks in the Apollo Router
Your router's CORS policy enables you to control which websites can talk to your server. In most cases, the browser checks your server's CORS policy by sending a preflight request before sending the actual operation. This is a separate HTTP request. Unlike most HTTP requests (which use the
POST method), this request uses a method called
OPTIONS. The browser sends an
Origin header, along with some other headers that start with
Access-Control-* headers describing its policies (as described above), and the browser uses that response to decide whether it's OK to send the real request. Processing the
OPTIONS preflight request never actually executes GraphQL operations.
However, in some circumstances, the browser will not send this preflight request. If the request is considered "simple", then the browser just sends the request without sending a preflight first. Your server's response can still contain
Unfortunately, this means that your server might execute GraphQL operations from "simple" requests sent by sites that shouldn't be allowed to communicate with your server. And these requests can even contain cookies! Although the browser will hide your server's response data from the malicious code, that might not be sufficient. If running the operation has side effects, then the attacker might not care if it can read the response or not, as long as it can use an unsuspecting user's browser (and cookies!) to trigger those side effects. Even with a read-only query, the malicious code might be able to figure out something about the response based entirely on how long the query takes to execute.
Attacks that use simple requests for their side effects are called "cross-site request forgery" attacks, or CSRF. Attacks that measure the timing of simple requests are called "cross-site search" attacks, or XS-Search.
To avoid CSRF and XS-Search attacks, GraphQL servers should refuse to execute any operation coming from a browser that has not "preflighted" that operation. There's no reliable way to detect whether a request came from a browser, so GraphQL servers should not execute any operation in a "simple request".
The most important rule for whether or not a request is "simple" is whether it tries to set arbitrary HTTP request headers. Any request that sets the
Content-Type header to
application/json (or anything other than a list of three particular values) cannot be a simple request, and thus it must be preflighted. Because all
POST requests recognized by Apollo Server must contain a
Content-Type header specifying
application/json, we can be confident that they are not simple requests and that if they come from a browser, they have been preflighted.
However, Apollo Router also handles
GET requests which do not require a
Content-Type header, so they can potentially be simple requests. So how can we ensure that we only execute
GET requests that are not simple requests? If we require the request to include an HTTP header that is never set automatically by the browser, then that is sufficient: requests that set HTTP headers other than the handful defined in the spec must be preflighted.
Apollo Router 0.9 introduced a CSRF prevention feature, which is enabled by default. When this feature is enabled, Apollo Router only executes GraphQL operations if at least one of the following conditions is true:
- The incoming request includes a
Content-Typeheader that specifies a type other than
multipart/form-data. Notably, a
application/json(including any suffix like
application/json; charset=utf-8) is sufficient. This means that all
POSTrequests (which must use
Content-Type: application/json) will be executed. Additionally, all versions of Apollo Client Web that support
GETrequests do include
Content-Type: application/jsonheaders, so any request from Apollo Client Web (
GET) will be executed.
- There is a
X-Apollo-Operation-Nameheader. This header is sent with all operations (
GET) by Apollo iOS (v0.13.0+) and Apollo Kotlin (all versions, including its former name "Apollo Android"), so any request from Apollo iOS or Apollo Kotlin will be executed.
- There is a
- All HTTP header names are case-insensitive.
- Unlike requests that will execute GraphQL operations, CSRF prevention is not applied to the landing page or to health checks. It does however apply to new endpoints added by plugins.
HTTP requests that satisfy none of the conditions above will be rejected with a 400 status code and a message clearly explaining which headers need to be added in order to make the request succeed.
This should have no impact on legitimate use of your graph, unless you have clients that send
GET requests and are not Apollo Client Web, Apollo iOS, or Apollo Kotlin. If you do send
GET requests with other clients, you should configure them to send a non-empty
Apollo-Require-Preflight header along with all requests.
You can also configure the set of headers that allow execution. For example, if you use a GraphQL client that performs
GET requests without sending
Apollo-Require-Preflight headers, but it does send a
csrf:required_headers:- X-Apollo-Operation-Name- Apollo-Require-Preflight- Some-Special-Header
The check for
Content-Type remains the same.
We highly recommend that you leave CSRF prevention enabled. However it is still possible to disable the plugin entirely:
This could be appropriate for a GraphQL server that only contains public data and allows no mutation, or on a closed private network where browsers cannot reach untrusted websites.