How severe is CVE-2026-11718?

CVE-2026-11718 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.

Is CVE-2026-11718 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (8th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-11718?

CVE-2026-11718 affects Google Mcp Toolbox For Databases. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-11718?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

Does CVE-2026-11718 have an EU (EUVD) identifier?

Yes. CVE-2026-11718 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-37880.

When was CVE-2026-11718 published?

CVE-2026-11718 was published on 2026-06-18 and last updated on 2026-08-17.

CVE-2026-11718

CVE-2026-11718 is a critical-severity vulnerability in Google Mcp Toolbox For Databases with a CVSS 3.x base score of 9.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-287.

Key facts

Severity: Critical (CVSS 3.x base score 9.1)
CVSS v4: 9.3
EPSS exploit prediction: 0% (8th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-37880
Weakness: CWE-287
Affected product: Google Mcp Toolbox For Databases
Published: 2026-06-18
Last modified: 2026-08-17

Description

An authentication bypass vulnerability exists in the generic opaque token validation path (validateOpaqueToken) of googleapis/mcp-toolbox. When the toolbox validates an opaque token via an OAuth 2.0 introspection endpoint (RFC 7662), it decodes the response into an introspectResp struct. However, the subsequent claim-checking logic (validateClaims) evaluates the issuer condition as if a.issuer != "" && iss != "". If the external OAuth provider's introspection response omits the optional iss (issuer) field completely, the variable iss defaults to an empty string. This causes the conditional block to evaluate to false and be skipped silently. Consequently, the application accepts tokens issued by unauthorized or unintended third-party identity providers.

Frequently asked questions

What is CVE-2026-11718?: An authentication bypass vulnerability exists in the generic opaque token validation path (validateOpaqueToken) of googleapis/mcp-toolbox. When the toolbox validates an opaque token via an OAuth 2.0 introspection endpoint (RFC 7662), it decodes the response into an introspectResp struct. However, the subsequent claim-checking logic (validateClaims) evaluates the issuer condition as if a.issuer != "" && iss != "". If the external OAuth provider's introspection response omits the optional iss (issuer) field completely, the variable iss defaults to an empty string. This causes the conditional block to evaluate to false and be skipped silently. Consequently, the application accepts tokens issued by unauthorized or unintended third-party identity providers.
How severe is CVE-2026-11718?: CVE-2026-11718 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2026-11718 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (8th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-11718?: CVE-2026-11718 affects Google Mcp Toolbox For Databases. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-11718?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
Does CVE-2026-11718 have an EU (EUVD) identifier?: Yes. CVE-2026-11718 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-37880.
When was CVE-2026-11718 published?: CVE-2026-11718 was published on 2026-06-18 and last updated on 2026-08-17.

References

https://github.com/googleapis/mcp-toolbox/pull/3360

Affected products (1)

cpe:2.3:a:google:mcp_toolbox_for_databases:*:*:*:*:*:*:*:*

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