An authentication bypass vulnerability exists in the generic opaque token validation path (validateOpaqueToken) of googleapis/mcp-toolbox.
Exact source revision recorded 3 Nov 2026 03:08:01 UTC. It does not establish the source's current position. Latest evidence.
euvd · EUVD-2026-37879
PublishedAn 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.
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Original publisher date fields
datePublished: Jun 18, 2026, 11:50:23 AM
dateUpdated: Jun 18, 2026, 12:23:15 PM
- Source published
- Jun 18, 2026, 11:50:23 AM (timezone not stated)
- Source modified
- Jun 18, 2026, 12:23:15 PM (timezone not stated)
- Observed here
- 3 Nov 2026 03:08:01 UTC
- Source terms
- ENISA EUVD · source terms and attribution apply
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EUVD CVSS 4.0 · 9.3 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