Critical Authentication

CVE-2026-11718 — Google MCP Toolbox for Databases: authentication bypass in opaque token issuer validation

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.

Published Jun 18, 2026 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: Google

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

EPSS 0.2% (30-day exploitation probability)+1
Technical severity (critical)+10
Automatable exploitation (SSVC)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

0.19%

ahead of 8% of scored CVEs · Oct 15, 2026

Affects

Google

Mcp Toolbox For Databases and 1 more

CVSS base

9.1

Critical · 3 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation

None

none · proof-of-concept · active

Automatable

Yes

can an attacker script the kill-chain steps

Technical impact

Total

partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

Documented patch — github.com (NIST National Vulnerability Database)

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Google Mcp Toolbox For Databases, Google MCP Toolbox for Databases (googleapis/mcp-toolbox)).
The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
Apply the fixed version or the patch documented under Remediation.
Search available logs for exploit probes matching the vulnerability class (authentication), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Google	Mcp Toolbox For Databases	≥ 1.0.0 and ≤ 1.3.0	Vulnerable	NIST National Vulnerability Database
Google	MCP Toolbox for Databases (googleapis/mcp-toolbox)	≥ 1.0.0 and ≤ 1.3.0	Vulnerable	CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Network

Attack complexity

Low

Privileges required

None

User interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

None

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
9.3	CVSS 4.0	Critical	—	—	cve-coordination@google.com via NIST National Vulnerability Database
9.3	CVSS 4.0	Critical	—	—	Google via CVE Program (cve.org) e CISA ADP
9.1	CVSS 3.1	Critical	3.9	5.2	nvd@nist.gov via NIST National Vulnerability Database

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N (score shown at the top: nvd@nist.gov)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-287 · Improper Authentication

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 15, 2026 · 3 reading(s) · max 0.19%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
Review authentication logs: logins without MFA, anomalous sessions and recently created accounts.

web/proxy/WAF logsnetwork IDS/IPSauthentication logs

Analysis and videos

CVE-2026-11718: Google MCP Toolbox for Databases: authentication bypass in opaque token issuer validation
CVE-2026-11718 is a critical authentication bypass (CWE-287) in Google MCP Toolbox for Databases (googleapis/mcp-toolbox), affecting versions 1.0.0 through 1.3.0. When an OAuth 2.0 introspection response omits the optional iss field, the issuer check is silently skipped, so tokens from unintended identity providers can be accepted. A patch is available via GitHub pull request 3360, and no confirmed exploitation appears in the sources consulted.

Timeline

What happened to this CVE, newest first.

2026
Affected products added · google/mcp toolbox for databases (googleapis/mcp-toolbox)
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
SSVC assessment updated
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 13, 2026
Fix documented
Oct 13, 2026 · NIST National Vulnerability Database
CVSS changed · 9.1
Oct 13, 2026 · NIST National Vulnerability Database
Source status changed · → Analyzed
Oct 13, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 13, 2026 · NIST National Vulnerability Database
CVE published
Jun 18, 2026 · Google

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

1 on the record

github.com/googleapis/mcp-toolbox/pull/3360
Patch, NIST National Vulnerability Database

Elsewhere on this site

Google
every CVE for this vendor

Authentication
same class

CWE-287
other pages naming this weakness

Related CVEs (same products)

High CVE-2026-102242 Path Traversal via Symlink Following in allowedLocalRoots in MCP Toolbox for Databases 16d
High CVE-2026-14541 Authentication Bypass and Audience Confusion in MCP Toolbox OAuth Provider Jul 31, 2026
Medium CVE-2026-14540 Server-Side Request Forgery via Unrestricted HTTP Redirection in MCP Toolbox Jul 30, 2026
High CVE-2026-14538 BigQuery Dataset Allowlist Bypass via Metadata Dry-Run in MCP Toolbox Jul 30, 2026
High CVE-2026-14539 Denial of Service via Unrestricted Payload Buffering in MCP Toolbox Jul 30, 2026
Critical CVE-2026-14537 Authorization Bypass in MCP Toolbox Legacy HTTP Endpoints Jul 30, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-11718 is "Google MCP Toolbox for Databases: authentication bypass in opaque token issuer validation", rated Critical. It affects Mcp Toolbox For Databases (Google); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 9.1 describes technical severity. EPSS 0.19% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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