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Vulnerabilities

Vulnerability · CVE-2026-111770

MCP TypeScript server SDK: Shared transport or server instances delivered one HTTP client's messages to another

Published Oct 20, 2026 · catalog updated Oct 20, 2026 · MCP TypeScript server SDK:

Last checked Nov 6, 2026. A connected source was read within the last 7 days.

Open the advisory

Exploitation likelihood is not on this record for CVE-2026-111770. A missing EPSS score is not a low risk. Compare MCP TypeScript server SDK: with the linked advisory before you change production.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (MCP TypeScript server SDK:).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
  • EPSS is missing. A missing score is not a low risk.
Severity
High7.7
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
Not in the current FIRST EPSS dataset
Remediation
Version ranges on file
Affected products
npm @modelcontextprotocol/server · package npm

### Summary In affected versions, an MCP server reached over HTTP could deliver one client's responses and notifications to another client. This happened when clients shared one stateless transport, or one or instance. Messages were matched to a connection by JSON-RPC alone. SDK clients number requests from 0, so ids collide in normal use. ### Am I affected? Yes, if more than one client can reach your HTTP endpoint and your code creates the transport or the server once at startup, instead of once per request or per session. Until this release, the README examples of , , and showed that pattern. Affected versions: 2.0.0 through 2.2.0. Not affected: - with a factory that builds a new server on every call - stdio servers - 1.26.0 and later ### Fix Upgrade to 2.3.0 or later. **You also need to change your code.** The SDK now refuses to be shared, so an affected app fails requests after upgrading: a second rejects with , and a stateless transport rejects its second request. Change to one of these: - ** :** pass a factory that builds a new on every call. - **Per request:** build a new and a new transport inside the request handler. - **Per session:** set and keep one and one transport per session. If you cannot upgrade yet, the same change fixes affected versions.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • npm @modelcontextprotocol/server>= 2.0.0, < 2.3.0
  • package npmversion unspecified

How to fix CVE-2026-111770

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

Exploitation likelihood is not on this record for CVE-2026-111770. A missing EPSS score is not a low risk. Compare MCP TypeScript server SDK: with the linked advisory before you change production.

Which versions are affected?

Compare what you have installed with >= 2.0.0, < 2.3.0. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-362: Race Condition. EPSS is absent from the current FIRST dataset. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Oct 20, 2026 · GitHub Advisory Database

    Detected

    ### Summary In affected versions, an MCP server reached over HTTP could deliver one client's responses and notifications to another client. This happened when clients shared one stateless transport, or one or instance. Messages were matched to a connection by JSON-RPC alone. SDK clients number requests from 0, so ids collide in normal use. ### Am I affected? Yes, if more than one client can reach

  2. Oct 20, 2026 · GitHub Advisory Database

    Updated

    ### Summary In affected versions, an MCP server reached over HTTP could deliver one client's responses and notifications to another client. This happened when clients shared one stateless transport, or one or instance. Messages were matched to a connection by JSON-RPC alone. SDK clients number requests from 0, so ids collide in normal use. ### Am I affected? Yes, if more than one client can reach

Sources

References

Freshness

Last verified in this catalog Nov 6, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • Snyk Vulnerability DatabaseOct 26, 2026
  • CVE.orgOct 22, 2026
  • GitHub Advisory DatabaseOct 21, 2026