An authentication bypass vulnerability exists in the generic opaque token validation path (validateOpaqueToken) of googleapis/mcp-toolbox.
When verifying an unparsed opaque token via an OAuth 2.0 introspection endpoint (RFC 7662), the toolbox decodes the response into an introspectResp struct where the Active field is declared as a pointer to a boolean (*bool). The code only explicitly rejects a token if the response contains a populated active field set to false (if introspectResp.Active != nil && !*introspectResp.Active). If an introspection endpoint responds with a payload that completely omits the mandatory active key, the internal variable remains nil, causing the conditional check to short-circuit. As a result, Toolbox accepts authorization tokens missing the "active" field, granting access to protected tools and underlying data sources.
Metrics
Affected Vendors & Products
References
| Link | Providers |
|---|---|
| https://github.com/googleapis/mcp-toolbox/pull/3341 |
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History
Thu, 18 Jun 2026 16:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | An authentication bypass vulnerability exists in the generic opaque token validation path (validateOpaqueToken) of googleapis/mcp-toolbox. When verifying an unparsed opaque token via an OAuth 2.0 introspection endpoint (RFC 7662), the toolbox decodes the response into an introspectResp struct where the Active field is declared as a pointer to a boolean (*bool). The code only explicitly rejects a token if the response contains a populated active field set to false (if introspectResp.Active != nil && !*introspectResp.Active). If an introspection endpoint responds with a payload that completely omits the mandatory active key, the internal variable remains nil, causing the conditional check to short-circuit. As a result, Toolbox accepts authorization tokens missing the "active" field, granting access to protected tools and underlying data sources. | |
| Weaknesses | CWE-287 | |
| References |
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| Metrics |
cvssV4_0
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Status: PUBLISHED
Assigner: Google
Published:
Updated: 2026-06-18T12:23:15.209Z
Reserved: 2026-06-09T00:41:54.835Z
Link: CVE-2026-11717
Updated: 2026-06-18T12:23:07.609Z
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OpenCVE Enrichment
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