Model Context Protocol Python SDK: Server bearer-token authentication accepts tokens issued for a different resource server

Exploitation

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

CVSS

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

EPSS

• CVE-2026-116684: 0.36% estimated exploitation activity in the next 30 days; percentile 30.41 (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 server-side bearer authentication had no way to check that a token was issued for your server (its audience). Where one authorization server issues tokens for several services, a valid token for another service was also accepted by your MCP server.

Am I affected? Yes, if your HTTP server uses the SDK's bearer authentication (`auth=AuthSettings(...)` with `token_verifier=`), its authorization server also issues tokens for other services, and your `TokenVerifier` does not check the token's audience (`aud`) itself. Affected versions: - `mcp` 1.10.0 through 1.29.1 - `mcp` 2.0.0 through 2.1.1

Fix Upgrade to: - 1.x: `mcp` 1.30.0 or later - 2.x: `mcp` 2.2.0 or later Upgrading alone changes nothing. The patched versions add a `validate_token_resource` setting that is off unless you set it. To turn the check on, make both of these changes together: 1. Set `validate_token_resource=True` in `AuthSettings`, with `resource_server_url` set to…

Published by the source

27 Oct 2026, 21:06 UTC

Last modified by the source

27 Oct 2026, 21:15 UTC

Source last checked

28 Oct 2026, 06:05 UTC

1. Revision 2 · amended · 28 Oct 2026

   Amended from osv record GHSA-w4fh-qvv9-3v23

2. Revision 1 · created · 27 Oct 2026

   Published from ghsa record GHSA-w4fh-qvv9-3v23

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# Patch Next advisory brief: CVE-2026-116684

Advisory: Model Context Protocol Python SDK: Server bearer-token authentication accepts tokens issued for a different resource server
IDs: CVE-2026-116684, GHSA-w4fh-qvv9-3v23
Record: https://patchnext.com/advisories/cve-2026-116684 (revision 2, source checked 28 Oct 2026, 06:05 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: mcp 2.2.0, 1.30.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI mcp: affected >= 2.0.0, < 2.2.0; >= 1.10.0, < 1.30.0; fixed in 2.2.0, 1.30.0

## Suggested inspection (read-only)
- `python -m pip show mcp`: prints the installed version. Run with the environment that serves production active.

## 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 mcp.
- 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://osv.dev/vulnerability/GHSA-w4fh-qvv9-3v23 (OSV record GHSA-w4fh-qvv9-3v23 lists affected ranges: PyPI mcp >=2.0.0 =1.10.0 <1.30.0 (fixed))
- Verified: https://github.com/advisories/GHSA-w4fh-qvv9-3v23 (GitHub-reviewed advisory GHSA-w4fh-qvv9-3v23 lists affected ranges: PyPI mcp >=2.0.0 =1.10.0 <1.30.0)

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