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CVE-2026-11720: MCP Toolbox HTTP tool path parameters allow traversal to unintended endpoints

criticalCVSS 4.0 9.3 · 3.1 9.1GHSA-vwxw-jrg6-9jxv

A path traversal vulnerability exists in the HTTP tool URL builder of googleapis/mcp-toolbox. When constructing downstream API requests, the URL builder substitutes user-controlled pathParams into the configured tool path and parses the resulting string as a relative URL. While it checks that the input does not alter the scheme, host, or user info, it relies on ResolveReference for the final URL resolution.

Published Jun 29, 2026 · Updated Sep 4, 2026

Affected packages

github.com/googleapis/mcp-toolbox

Ecosystem
Go
Affected
< 1.3.0
Fixed in
1.3.0
Check
go list -m github.com/googleapis/mcp-toolbox

Advisory details

From the GitHub Advisory Database (CC BY 4.0).

A path traversal vulnerability exists in the HTTP tool URL builder of googleapis/mcp-toolbox.

When constructing downstream API requests, the URL builder substitutes user-controlled pathParams into the configured tool path and parses the resulting string as a relative URL. While it checks that the input does not alter the scheme, host, or user info, it relies on ResolveReference for the final URL resolution. Because dot segments (../) are normalized during this resolution step, an attacker can supply path parameters containing directory traversal sequences to escape the operator-configured path scope. This allows the client to coerce the toolbox into making requests to unintended endpoints on the same target host while forwarding the toolbox's configured credentials (e.g., bypassing a restricted path like /api/v1/users/{{.id}} to reach /admin/secrets).

References

How this page is made: the data panel comes from the GitHub Advisory Database, CISA’s KEV catalog, the NVD and FIRST EPSS, and updates twice a day. No analysis has been written for this entry yet. Methodology

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