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CVE-2026-11720 – Path Traversal / Credential-Forwarding SSRF – Google MCP Toolbox for Databases b…

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Summary

CVE-2026-11720 is a critical path traversal vulnerability (CWE-22) in the HTTP tool URL builder of Google’s MCP Toolbox for Databases (googleapis/mcp-toolbox), carrying a CVSS 4.0 score of 9.3 (Critical). The flaw allows an unauthenticated remote attacker to supply dot-segment sequences (../) in path parameters that are silently normalized by Go’s ResolveReference during URL construction, enabling the attacker to coerce the toolbox into making requests to arbitrary endpoints on the configured target host while forwarding the toolbox’s own credentials. All versions of MCP Toolbox for Databases prior to 1.3.0 are affected; a fix was released on May 21, 2026.

Technical details

  • Root cause: When constructing downstream API requests, the HTTP tool URL builder substitutes user-controlled pathParams into the operator-configured tool path and parses the result as a relative URL. The code validates that user input does not change the scheme, host, or user-info components, but delegates final URL resolution to Go’s net/url.ResolveReference. Because ResolveReference normalizes dot segments (../, %2e%2e/) during resolution, this validation check is silently bypassed.
  • Trigger conditions: Any HTTP-type tool that exposes a path parameter template (e.g., /api/v1/users/{{.id}}) can be targeted. No authentication, privileges, or user interaction are required to trigger the vulnerability (CVSS 4.0: PR:N, UI:N).
  • Attack vector: Network (AV:N). An attacker sends a crafted MCP tool call containing path traversal sequences (e.g., ../../admin/secrets) in a path parameter. The toolbox resolves the path and issues an HTTP request to the traversed endpoint on the same configured target host.
  • Impact: The toolbox forwards its configured credentials (e.g., API keys, bearer tokens, IAM identities) to the attacker-chosen endpoint, exposing sensitive backend resources such as administrative APIs or secret stores. Both confidentiality and integrity are rated High (VC:H, VI:H) in the CVSS 4.0 vector.

Affected software

  • Google MCP Toolbox for Databases (googleapis/mcp-toolbox) — all versions before 1.3.0

Severity

  • CVSS 4.0 Base Score: 9.3 (Critical)
  • Vector String: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate action — upgrade: Update to MCP Toolbox for Databases v1.3.0 or later (released May 21, 2026). The fix, introduced in PR #3218, rejects relative and URL-encoded dot segments (.., %2e%2e) in path parameters and enforces that resolved paths cannot escape the configured base path scope. It also introduces PathEscape and QueryEscape template functions for additional input hardening.
  • If immediate patching is not possible: Restrict network access to the MCP Toolbox HTTP endpoint so it is not reachable from untrusted networks. Audit all HTTP-type tool definitions that expose path parameter templates and, where feasible, disable those tools until the upgrade can be applied.
  • Defense in depth: Ensure that backend systems receiving requests from the toolbox apply their own authorization controls independently of the path the toolbox forwards, limiting the blast radius if a traversal attempt succeeds.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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