CVE-2026-104852

GraphQL Tools provides utilities for building, stitching, and mocking GraphQL schemas. Prior to 12.0.1, the GraphQL Tools utils package's mergeDeep function follows inherited properties while recursively merging source objects and does not exclude proto, constructor, or prototype keys. An unauthenticated GraphQL client can alias fields to those names so responses from two subgraphs collide during ordinary supergraph result merging, causing mergeDeep to traverse Object and Function prototypes and overwrite Function.prototype.call with a subgraph-supplied value. This breaks subsequent requests in the process until restart. This issue is fixed in version 12.0.1.

GraphQL Tools provides utilities for building, stitching, and mocking GraphQL schemas. Prior to 12.0.1, the GraphQL Tools utils package's mergeDeep function follows inherited properties while recursively merging source objects and does not exclude proto, constructor, or prototype keys. An unauthenticated GraphQL client can alias fields to those names so responses from two subgraphs collide during ordinary supergraph result merging, causing mergeDeep to traverse Object and Function prototypes and overwrite Function.prototype.call with a subgraph-supplied value. This breaks subsequent requests in the process until restart. This issue is fixed in version 12.0.1.

Closed by https://github.com/ardatan/graphql-tools/pull/8423 Mitigated in Hive Gateway by https://github.com/graphql-hive/gateway/pull/2600

A client can alias fields to constructor, __proto__ or prototype so that the response keys from two subgraphs collide on those names during result merging. Because mergeDeep recursed through inherited properties, the merge walked {}.constructor to Object, then Object.__proto__ to Function.prototype, and wrote a subgraph-supplied value over Function.prototype.call, breaking every subsequent request in the process until restart. This is remotely triggerable by an unauthenticated client with a single query against any supergraph that merges an object from two subgraphs, which is the ordinary @shareable or entity case, so it is a denial of service rather than a theoretical hardening issue.

{
  shared {
    fieldA
    constructor: fieldB {
      __proto__: child {
        call: value
      }
    }
  }
}

GraphQL Tools provides utilities for building, stitching, and mocking GraphQL schemas. Prior to 12.0.1, the GraphQL Tools utils package's mergeDeep function follows inherited properties while recursively merging source objects and does not exclude proto, constructor, or prototype keys. An unauthenticated GraphQL client can alias fields to those names so responses from two subgraphs collide during ordinary supergraph result merging, causing mergeDeep to traverse Object and Function prototypes and overwrite Function.prototype.call with a subgraph-supplied value. This breaks subsequent requests in the process until restart. This issue is fixed in version 12.0.1.

GraphQL Tools provides utilities for building, stitching, and mocking GraphQL schemas. Prior to 12.0.1, the GraphQL Tools utils package's mergeDeep function follows inherited properties while recursively merging source objects and does not exclude proto, constructor, or prototype keys. An unauthenticated GraphQL client can alias fields to those names so responses from two subgraphs collide during ordinary supergraph result merging, causing mergeDeep to traverse Object and Function prototypes and overwrite Function.prototype.call with a subgraph-supplied value. This breaks subsequent requests in the process until restart. This issue is fixed in version 12.0.1.

Closed by https://github.com/ardatan/graphql-tools/pull/8423 Mitigated in Hive Gateway by https://github.com/graphql-hive/gateway/pull/2600

A client can alias fields to constructor, __proto__ or prototype so that the response keys from two subgraphs collide on those names during result merging. Because mergeDeep recursed through inherited properties, the merge walked {}.constructor to Object, then Object.__proto__ to Function.prototype, and wrote a subgraph-supplied value over Function.prototype.call, breaking every subsequent request in the process until restart. This is remotely triggerable by an unauthenticated client with a single query against any supergraph that merges an object from two subgraphs, which is the ordinary @shareable or entity case, so it is a denial of service rather than a theoretical hardening issue.

{
  shared {
    fieldA
    constructor: fieldB {
      __proto__: child {
        call: value
      }
    }
  }
}