GraphQL Tools provides utilities for building, stitching, and mocking GraphQL schemas. From 10.10.1 until 12.0.2, the @graphql-tools/utils mergeIncrementalResult helper passes incrementalResult.path segments to setObjectKeyPath without runtime primitive-type validation. A non-primitive segment can bypass strict comparisons against __proto__, constructor, and prototype, then be coerced during property access so a malicious or compromised upstream incremental GraphQL response writes attacker-controlled properties to Object.prototype in the consuming Node.js process. The affected implementation is packages/utils/src/mergeIncrementalResult.ts and is reachable when consumers merge untrusted @defer or @stream transport results. This issue is fixed in version 12.0.2.