Origin Validation Error Affecting mcphost package, versions <0.34.0-160000.4.1


Severity

Recommended
0.0
medium
0
10

Based on SUSE Linux Enterprise Server security rating.

Threat Intelligence

EPSS
0.22% (12th percentile)

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  • Snyk IDSNYK-SLES1600-MCPHOST-20261716
  • published29 Sept 2026
  • disclosed6 Sept 2026

Introduced: 6 Sep 2026

CVE-2026-81092  (opens in a new tab)
CWE-346  (opens in a new tab)

How to fix?

Upgrade SLES:16.0.0 mcphost to version 0.34.0-160000.4.1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream mcphost package and not the mcphost package as distributed by SLES. See How to fix? for SLES:16.0.0 relevant fixed versions and status.

mcp-go accepted requests on its HTTP transports without checking the Host header. StreamableHTTPServer.ServeHTTP in server/streamable_http.go and SSEServer.ServeHTTP in server/sse.go served any request arriving over a loopback connection regardless of the host it named, and the SSE transport's cross-origin default allowed any origin. A page in a browser could therefore point a name it controlled at the loopback address and reach a server listening there, invoking tools and reading resources that the server exposed on the assumption that only local software could connect. No release before 0.56.0 validated the header on either transport; 0.56.0 adds server/http_localhost.go, which rejects a loopback-bound request carrying a host that is not a loopback name, and wires it into both transports.

CVSS Base Scores

version 3.1