GraphiQL is an in-browser tool that leverages the GraphQL schema introspection mechanism to provide a graphical interface for GraphQL API development and testing. GraphiQL assists users in exploring GraphQL schemas as well as composing and executing GraphQL queries.

Allowing access to GraphiQL in production is not recommended because enabling introspection of your GraphQL schemas through GraphiQL can pose a risk to your overall security posture. An attacker can use GraphiQL and introspection to obtain implementation details from a GraphQL schema that enables them to perform a more targeted attack. GraphQL schemas can leak information such as internally used fields, descriptions, and deprecation notes that might not be intended for public consumption.

Example 1: The following code initializes a GraphQL.js endpoint with GraphiQL enabled by default:

app.use('/graphql', graphqlHTTP({
    schema
}));

The GraphQL introspection capability enables anyone to query a GraphQL server for information about the current schema. An interested party can issue GraphQL introspection queries to retrieve a complete view of a schema's available operations, data types, fields, and documentation.

GraphQL introspection offers a significant utility in the context of developing and sharing information about GraphQL APIs. Introspection is a powerful GraphQL feature that can facilitate integration with various tools. For example, an IDE can leverage schema introspection to provide enhanced features for developing and testing GraphQL APIs.

However, allowing anyone to query your GraphQL schemas in production can pose a risk to your overall security posture. An attacker can use introspection to obtain implementation details from a GraphQL schema that enables them to perform a more targeted attack. GraphQL schemas can leak information such as internally used fields, descriptions, and deprecation notes that might not be intended for public consumption.

Example 1: The following code initializes a Hot Chocolate GraphQL endpoint with schema introspection enabled by default:

    services
        .AddGraphQLServer()
        .AddQueryType<Query>()
        .AddMutationType<Mutation>();
    

Including executable content from another web site is a risky proposition. It ties the security of your site to the security of the other site.

Example: Consider the following script tag.

  <script src="http://www.example.com/js/fancyWidget.js"></script>

If this tag appears on a web site other than www.example.com, then the site is dependent upon www.example.com to serve up correct and non-malicious code. If attackers can compromise www.example.com, then they can alter the contents of fancyWidget.js to subvert the security of the site. They could, for example, add code to fancyWidget.js to steal a user's confidential data.

Programmers often trust the contents of hidden fields, expecting that users will not be able to view them or manipulate their contents. Attackers will violate these assumptions. They will examine the values written to hidden fields and alter them or replace the contents with attack data.

Example:

  Hidden hidden = new Hidden(element);

If hidden fields carry sensitive information, this information will be cached the same way the rest of the page is cached. This can lead to sensitive information being tucked away in the browser cache without the user's knowledge.

Cross-Origin Resource Sharing, commonly referred to as CORS, is a technology that allows a domain to define a policy for its resources to be accessed by a web page hosted on a different domain using cross domain XML HTTP Requests (XHR). Historically, the browsers have restricted XHR requests to abide by the same origin policy. This policy sets the script execution scope to the resources available on the current domain and prohibits any communication to domains outside this scope. However, a few HTML tags, such as SCRIPT, IMG, and IFRAME, are exempt from the same origin policy and allow remote content to be loaded from a different domain. These are secure alternatives for the site that loads contents from remote domain and no special permission or cross-domain policy is required from hosting domain.
While CORS is supported on all major browsers, it also requires that the domain correctly defines the CORS policy in order to have its resources shared with another domain. These restrictions are managed by access policies typically communicated in specialized response headers, such as:

- Access-Control-Allow-Origin
- Access-Control-Allow-Headers
- Access-Control-Allow-Methods

However, caution should be taken when defining these headers because an overly permissive policy configured at server level for domain or directory on a domain can open more content for cross domains access than intended. CORS can allow a malicious application to communicate with victim application in an inappropriate way leading to information disclosure, spoofing, data theft, relay or other attacks.
Implementing CORS can increase an application's attack surface and should be used only when necessary.

Cross-Origin Resource Sharing, commonly referred to as CORS, is a technology that allows a domain to define a policy for its resources to be accessed by a web page hosted on a different domain using cross domain XML HTTP Requests (XHR). Historically, the browser restricts cross domain XHR requests to abide by the same origin policy. At its basic form, the same origin policy sets the script execution scope to the resources available on the current domain and prohibits any communication to domains outside this scope. Therefore, execution and incorporation of remote methods and functions hosted on domains outside of the current domain are effectively prohibited. While CORS is supported on all major browsers, it also requires that the domain correctly defines the CORS policy in order to have its resources shared with another domain. These restrictions are managed by access policies typically included in specialized response headers, such as:

- Access-Control-Allow-Origin
- Access-Control-Allow-Headers
- Access-Control-Allow-Methods
- Access-Control-Max-Age

The browser generates a preflight OPTIONS request whenever the cross domain request made by the web page is anything other than a simple HTTP request. A GET or POST HTTP request with no special headers or credentials is considered a simple request. A response for a preflight request exposes the server's CORS policy via specialized headers mentioned above. After examining the required permissions, the browser makes the actual request that the web page initially performed. This extra preflight request adds overhead and hence the server can configure its preflight response to be cached.
Prolonged caching of a preflight response can pose a security threat as the policy can be updated on the server while a browser will still allow unauthorized access to resources based on the original cached policy. The time a response is allowed to be cached is conveyed using an Access-Control-Max-Age response header and a value more than 30 minutes is considered to be prolonged.

The Access-Control-Allow-Methods header, as reflected in the preflight response for the requested resource, indicates that it allows unsafe HTTP methods. An attacker can use HTTP methods such as PUT or DELETE to make unexpected modifications to shared resource and pose a security threat to the overall site security. A user agent rejects any request for this resource with an HTTP method other than the ones that are listed in the Access-Control-Allow-Methods response header.
Cross-Origin Resource Sharing, commonly referred to as CORS, is a technology that allows a domain to define a policy for its resources to be accessed by a web page hosted on a different domain using cross domain XML HTTP Requests (XHR). Historically, the browser restricts cross domain XHR requests to abide by the same origin policy. At its basic form, the same origin policy sets the script execution scope to the resources available on the current domain and prohibits any communication to domains outside this scope. Therefore, execution and incorporation of remote methods and functions hosted on domains outside of the current domain are effectively prohibited. While CORS is supported on all major browsers, it also requires that the domain correctly defines the CORS policy in order to have its resources shared with another domain. These restrictions are managed by access policies typically included in specialized response headers, such as:

- Access-Control-Allow-Origin
- Access-Control-Allow-Headers
- Access-Control-Allow-Methods