MCP TypeScript client SDK: HTTP client transports and OAuth requests followed cross-origin redirects and re-sent custom headers and request bodies

Exploitation

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

CVSS

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

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

Summary In affected versions, the SDK's HTTP client transports and OAuth requests followed redirects to any origin. If an MCP server or authorization server redirected a request to another origin, that origin received custom request headers (such as an X-API-Key set in requestInit.headers) and the mcp-session-id header. On a 307 or 308 it also received the request body, including OAuth token requests with their refreshtoken and clientsecret. On current runtimes fetch already drops the Authorization header across origins. Am I affected? Yes, if your application uses StreamableHTTPClientTransport, SSEClientTransport, or the SDK's OAuth client functions such as auth(). stdio clients are not affected. Affected versions: - @modelcontextprotocol/sdk all versions through 1.31.0 - @modelcontextprotocol/client 2.0.0 through 2.2.0 Fix Upgrade to: - 1.x: @modelcontextprotocol/sdk 1.32.0 or later - 2.x: @modelcontextprotocol/client 2.3.0 or later Redirects are now followed only within the same…

Published by the source

20 Oct 2026, 18:26 UTC

Last modified by the source

3 Nov 2026, 22:10 UTC

Source last checked

3 Nov 2026, 22:20 UTC

1. Revision 4 · amended · 3 Nov 2026

   Amended from ghsa record GHSA-6prh-2h8m-c8cw

2. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-6prh-2h8m-c8cw

3. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-6prh-2h8m-c8cw

4. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-6prh-2h8m-c8cw

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-111769

Advisory: MCP TypeScript client SDK: HTTP client transports and OAuth requests followed cross-origin redirects and re-sent custom headers and request bodies
IDs: CVE-2026-111769, GHSA-6prh-2h8m-c8cw
Record: https://patchnext.com/advisories/cve-2026-111769 (revision 4, source checked 3 Nov 2026, 22:20 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @modelcontextprotocol/sdk 1.32.0; @modelcontextprotocol/client 2.3.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @modelcontextprotocol/sdk: affected < 1.32.0; fixed in 1.32.0
- npm @modelcontextprotocol/client: affected >= 2.0.0, < 2.3.0; fixed in 2.3.0

## 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-6prh-2h8m-c8cw (GitHub-reviewed advisory GHSA-6prh-2h8m-c8cw lists affected ranges: npm @modelcontextprotocol/sdk >=0 =2.0.0 <2.3.0)
- Verified: https://osv.dev/vulnerability/GHSA-6prh-2h8m-c8cw (OSV record GHSA-6prh-2h8m-c8cw lists affected ranges: npm @modelcontextprotocol/sdk >=0 =2.0.0 <2.3.0 (fixed))

Commands are suggestions: review each one before running it.