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Response snapshot Oct 27, 2026, 03:11 UTC

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VulnerabilityCVE-2026-111769

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

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.

At a glance

Exploited
Not known
Severity
6.5 Medium (CVSS 3.1)
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: @modelcontextprotocol/sdk: 1.32.0; @modelcontextprotocol/client: 2.3.0. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-6prh-2h8m-c8cw (opens a new tab)

What happened

### 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 `refresh_token` and `client_secret`.

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.

Continue reading

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 origin, and not at all in browsers. If your MCP server or authorization server redirects to another origin on purpose, configure the final URL instead. Setting `redirectPolicy: 'follow'` on a transport restores the old behaviour and the exposure.

If a redirect may have reached a host you do not control, rotate the API keys and `client_secret` your application held and revoke its tokens.

If you cannot upgrade yet, pass a `fetch` that refuses redirects, for example `(url, init) => fetch(url, { ...init, redirect: 'error' })`.

Affected package ranges reported by GitHub: @modelcontextprotocol/sdk: < 1.32.0 @modelcontextprotocol/client: >= 2.0.0, < 2.3.0

Scores and how they were measured

CVSS base severity

6.5

Version 3.1As of

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

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

Not available

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-6prh-2h8m-c8cw (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-6prh-2h8m-c8cw, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-6prh-2h8m-c8cw, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  4. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-6prh-2h8m-c8cw, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  5. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-6prh-2h8m-c8cw, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  6. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-6prh-2h8m-c8cw, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  7. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-6prh-2h8m-c8cw, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  8. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-6prh-2h8m-c8cw, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  9. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-6prh-2h8m-c8cw, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  10. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-6prh-2h8m-c8cw, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 20). MCP TypeScript client SDK: HTTP client transports and OAuth requests followed cross-origin redirects and re-sent custom headers and request bodies (CVE-2026-111769). https://kevwire.com/record/CVE-2026-111769

MLA

"MCP TypeScript client SDK: HTTP client transports and OAuth requests followed cross-origin redirects and re-sent custom headers and request bodies (CVE-2026-111769)." KEVWire, 20 Oct. 2026, kevwire.com/record/CVE-2026-111769.

Chicago

KEVWire. "MCP TypeScript client SDK: HTTP client transports and OAuth requests followed cross-origin redirects and re-sent custom headers and request bodies (CVE-2026-111769)." Last modified October 20, 2026. https://kevwire.com/record/CVE-2026-111769.

Evidence summary (plain text)

MCP TypeScript client SDK: HTTP client transports and OAuth requests followed cross-origin redirects and re-sent custom headers and request bodies (Oct 20, 2026).
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 `refresh_token` and `client_secret`.

On current runtimes `fetch` already drops the `Authorization` header across origins.
CVSS 6.5 (version 3.1; evidence as of Oct 20, 2026; https://github.com/advisories/GHSA-6prh-2h8m-c8cw).
Sources:
GitHub-reviewed advisory GHSA-6prh-2h8m-c8cw: https://github.com/advisories/GHSA-6prh-2h8m-c8cw
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMlQxNDowNjoxNFrOAAfxZw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMlQwODoyNzoyM1rOAAYp9A%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMTozNTo1OFrOAAfwCQ%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMTozMDoxM1rOAAfv2A%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMToyODowOVrOAAfv1g%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMToyNDoyMFrOAAfv1Q%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMDo0NTowN1rOAAfvzQ%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMDozMDoyNlrOAAfvxw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMDowMzo1N1rOAAfvxQ%3D%3D
Record ID: CVE-2026-111769.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 26, 2026, 20:50 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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