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2026-02-04 — @modelcontextprotocol/sdk cross-client data leak via shared server instance reuse (GHSA-345p-7cg4-v4c7)

Product: @modelcontextprotocol/sdk (Model Context Protocol SDK)

Impact (per advisory): A server/transport instance reused across multiple clients can cause cross-client data exposure (data intended for one client could be received by another).

This matters most when: - multiple untrusted tenants/users connect to the same MCP server, or - you multiplex multiple client sessions through a shared transport.

  • Upgrade to a fixed version per the advisory.
  • Do not reuse a single server/transport instance across clients unless the SDK explicitly guarantees isolation.
  • Add a regression test that:
  • creates two clients,
  • sends distinct prompts/requests,
  • asserts that responses/notifications never cross boundaries.
  • If you operate an MCP server as a service:
  • treat this as a data isolation issue and review logs/telemetry for cross-session leakage.
  • consider adding per-tenant process/container isolation for high-risk deployments.

References

Consolidation note

This is the canonical page for this topic. During the 2026-05-22 redundancy pass, overlapping pages were reduced to compatibility pointers:

  • alerts/2026-02-05-mcp-typescript-sdk-cross-client-data-leak-ghsa-345p-7cg4-v4c7.md