Windows-MCP: HTTP transports expose unauthenticated PowerShell control with wildcard CORS

Exploitation

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

CVSS 4.0

8.9 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:P · score source

EPSS

• CVE-2026-48989: 0.40% estimated exploitation activity in the next 30 days; percentile 33.92 (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.

HTTP transports expose unauthenticated PowerShell control with wildcard CORS There is an issue in the SSE and Streamable HTTP transport modes. The default stdio mode is not affected, but the documented HTTP modes expose the MCP control plane without authentication and add wildcard CORS handling around it. The same server exposes the PowerShell tool, which executes caller-controlled commands as the Windows user running Windows-MCP. Relevant source: - src/windowsmcp/main.py:37-42: httpmiddleware() installs OptionsMiddleware and CORSMiddleware with alloworigins=[""], allowmethods=[""], and allowheaders=[""]. - src/windowsmcp/main.py:45-72: OptionsMiddleware responds to every OPTIONS request with wildcard Access-Control-Allow-Origin, Access-Control-Allow-Methods, and Access-Control-Allow-Headers. - src/windowsmcp/main.py:75-113: buildmcp() constructs FastMCP(name="windows-mcp", ...) without an auth provider. - src/windowsmcp/main.py:139-151: both sse and streamable-http call mcp.run(...)…

Published by the source

21 May 2026, 16:46 UTC

Last modified by the source

13 Jul 2026, 16:43 UTC

Source last checked

26 Oct 2026, 13:46 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-vrxg-gm77-7q5g

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-vrxg-gm77-7q5g

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

# Patch Next advisory brief: CVE-2026-48989

Advisory: Windows-MCP: HTTP transports expose unauthenticated PowerShell control with wildcard CORS
IDs: CVE-2026-48989, GHSA-vrxg-gm77-7q5g
Record: https://patchnext.com/advisories/cve-2026-48989 (revision 3, source checked 26 Oct 2026, 13:46 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: windows-mcp 0.7.5. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI windows-mcp: affected < 0.7.5; fixed in 0.7.5

## Suggested inspection (read-only)
- `python -m pip show windows-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 windows-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-vrxg-gm77-7q5g (OSV record GHSA-vrxg-gm77-7q5g lists affected ranges: PyPI windows-mcp >=0 <0.7.5 (fixed))
- Verified: https://github.com/advisories/GHSA-vrxg-gm77-7q5g (GitHub-reviewed advisory GHSA-vrxg-gm77-7q5g lists affected ranges: PyPI windows-mcp >=0 <0.7.5)

Commands are suggestions: review each one before running it.