apollo-server-core vulnerable to URL-based XSS attack affecting IE11 on default landing page

Impact

The default landing page contained HTML to display a sample curl command which is made visible if the full landing page bundle could not be fetched from Apollo's CDN. The server's URL is directly interpolated into this command inside the browser from window.location.href. On some older browsers such as IE11, this value is not URI-encoded. On such browsers, opening a malicious URL pointing at an Apollo Router could cause execution of attacker-controlled JavaScript.

This only affects Apollo Server with the default landing page enabled. Old browsers visiting your server may be affected if ANY of these apply:

• You do not pass any landing page plugin to the plugins option of new ApolloServer.
• You pass ApolloServerPluginLandingPageLocalDefault() or ApolloServerPluginLandingPageProductionDefault() to the plugins option of new ApolloServer.

Browsers visiting your server are NOT affected if ANY of these apply:

• You pass ApolloServerPluginLandingPageDisabled() to the plugins option of new ApolloServer.
• You pass ApolloServerPluginLandingPageGraphQLPlayground() to the plugins option of new ApolloServer.
• You pass a custom plugin implementing the renderLandingPage hook to the plugins option of new ApolloServer.

This issue was introduced in v3.0.0 when the landing page feature was added.

Patches

To avoid this, the sample curl command has been removed in release 3.10.1.

Workarounds

Disabling the landing page removes the possibility of exploit:

import { ApolloServerPluginLandingPageDisabled } from 'apollo-server-core';

new ApolloServer({
  plugins: [ApolloServerPluginLandingPageDisabled()],
  // ...
});

See also

A similar issue exists in the landing page of Apollo Router. See the corresponding Apollo Router security advisory.

For more information

If you have any questions or comments about this advisory:

• Open an issue in the Apollo Server repository
• Email us at [email protected]

Credits

This issue was discovered by Adrian Denkiewicz of Doyensec.