MCP TypeScript SDK: OAuth client could send credentials to an authorization server chosen by the MCP server

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS

• CVE-2026-104850: 0.23% estimated exploitation activity in the next 30 days; percentile 13.33 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary In affected versions, the SDK's OAuth client let the MCP server decide which authorization server received the client's OAuth credentials. Credentials were not tied to the authorization server they belong to. A malicious or compromised MCP server could name its own authorization server. With no user interaction, the client would send it: - the refreshtoken and clientsecret stored from an earlier sign-in - the clientsecret or signed assertion configured on a bundled provider Am I affected? Yes, if both of these hold: - your application uses the SDK's OAuth client over HTTP, through any of: - an authProvider on a transport - the withOAuth() middleware - direct calls to auth() or fetchToken() - it may connect to an MCP server you do not fully trust while holding credentials for a legitimate authorization server Affected versions: - @modelcontextprotocol/sdk 1.12.0 through 1.30.1 - @modelcontextprotocol/client 2.0.0 through 2.1.0, only for: - bundled providers without…

Published by the source

6 Oct 2026, 15:35 UTC

Last modified by the source

6 Oct 2026, 15:46 UTC

Source last checked

26 Oct 2026, 13:06 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-6qxp-vccf-f47h

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-6qxp-vccf-f47h

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-6qxp-vccf-f47h

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# Patch Next advisory brief: CVE-2026-104850

Advisory: MCP TypeScript SDK: OAuth client could send credentials to an authorization server chosen by the MCP server
IDs: CVE-2026-104850, GHSA-6qxp-vccf-f47h
Record: https://patchnext.com/advisories/cve-2026-104850 (revision 3, source checked 26 Oct 2026, 13:06 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @modelcontextprotocol/sdk 1.31.0; @modelcontextprotocol/client 2.2.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @modelcontextprotocol/sdk: affected >= 1.12.0, < 1.31.0; fixed in 1.31.0
- npm @modelcontextprotocol/client: affected >= 2.0.0, < 2.2.0; fixed in 2.2.0

## Suggested inspection (read-only)
- `npm ls @modelcontextprotocol/sdk --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.
- `npm ls @modelcontextprotocol/client --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @modelcontextprotocol/sdk, @modelcontextprotocol/client.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-6qxp-vccf-f47h (GitHub-reviewed advisory GHSA-6qxp-vccf-f47h lists affected ranges: npm @modelcontextprotocol/sdk >=1.12.0 =2.0.0 <2.2.0)
- Verified: https://osv.dev/vulnerability/GHSA-6qxp-vccf-f47h (OSV record GHSA-6qxp-vccf-f47h lists affected ranges: npm @modelcontextprotocol/sdk >=1.12.0 =2.0.0 <2.2.0 (fixed))

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