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CVE-2026-104852 – Prototype Pollution / Denial of Service – GraphQL Tools (@graphql-tools/utils) ≤ 1

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Summary

CVE-2026-104852 is a prototype pollution vulnerability (CWE-1321) in the mergeDeep utility function shipped in @graphql-tools/utils, part of the widely used GraphQL Tools (ardatan/graphql-tools) library. An unauthenticated remote attacker can craft a GraphQL query that causes mergeDeep to merge attacker-controlled keys such as __proto__, constructor, or prototype into Object.prototype/Function.prototype, corrupting shared JavaScript runtime state. The issue carries a CVSS v4.0 base score of 8.2 (High) and results in a denial-of-service condition affecting the whole process, not just the originating request.

Technical details

  • Root cause: mergeDeep recursively merged source object keys into a target object without filtering dangerous keys (__proto__, constructor, prototype) and used the in operator (which traverses the prototype chain) rather than hasOwnProperty to decide whether a key already existed on the target.
  • Trigger conditions: In a federated/stitched GraphQL setup (supergraph), a client can alias response fields to names like __proto__ so that results returned from two different subgraphs collide during ordinary result merging. This causes the polluted key to be written onto a shared object prototype (e.g., Function.prototype.call).
  • Attack vector: Network-based, no authentication, and no special user interaction required (CVSS v4.0 vector: AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N). The attack requires some attacker-controlled conditions (AT:P) — i.e., a gateway that merges/stitches results from multiple subgraphs using the vulnerable merge logic.
  • Impact: Once a core prototype method (such as Function.prototype.call) is overwritten, subsequent, unrelated requests handled by the same Node.js process can fail or behave unpredictably until the process is restarted — resulting in a process-wide availability (denial-of-service) impact. The advisory records no confidentiality or integrity impact.

Affected software

  • @graphql-tools/utils versions up to and including 12.0.0
  • Any ardatan/graphql-tools packages and downstream consumers (e.g., GraphQL gateway/stitching tools) that depend on the vulnerable mergeDeep implementation in @graphql-tools/utils prior to the fix
  • Fixed in @graphql-tools/utils 12.0.1 and later (with additional hardening released in subsequent 12.0.x versions)

Severity

  • CVSS v4.0 Base Score: 8.2 (High)
  • Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
  • CWE-1321: Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution)

Mitigation and recommended actions

  • Immediate: Upgrade @graphql-tools/utils (and any dependent graphql-tools packages) to version 12.0.1 or later. The fix skips source keys named __proto__, constructor, or prototype at every recursion level in mergeDeep, and replaces the in operator check with hasOwnProperty so inherited properties can no longer be used as merge targets. Note that follow-up hardening releases (12.0.2 and 12.0.3) further closed related gaps in incremental-result path merging — upgrading to the latest 12.0.x release is recommended rather than stopping at 12.0.1.
  • If immediate patching is not possible:
    • Restrict or disable field aliasing to reserved prototype-related names (__proto__, constructor, prototype) at the gateway/proxy layer if such filtering capability exists.
    • Monitor and alert on unexpected process restarts or request failures in GraphQL gateway/stitching services, which may indicate active exploitation.
    • Limit exposure of federated/stitched GraphQL endpoints that merge results from multiple subgraphs to trusted networks where feasible, as the vulnerability specifically affects result-merging logic used in supergraph configurations.

References

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