Analyst readout for executives and security teams
Plain-English summary
CVE-2026-9739 is a critical DNS rebinding/CORS issue in Google MCP Toolbox for Databases when used with SSE under MCP specification v2024-11-05. A retained wildcard CORS header could let an attacker-controlled site interact with affected Toolbox SSE behavior after user interaction. Public sources do not state active exploitation or a fixed version.
Executive priority
Treat this as urgent for teams using MCP Toolbox with database access over SSE. The issue could expose sensitive database tooling paths if reachable from a user’s browser context. Prioritize inventory and vendor-guided remediation, but avoid assuming enterprise-wide exposure without confirming SSE usage.
Technical view
The source states the SSE initialization handler retained `Access-Control-Allow-Origin: *` despite new `allowed-origins` and `allowed-hosts` flags. The weakness maps to CWE-942 and carries CVSS 4.0 score 9.4. The described impact is limited to Toolbox connections using SSE under spec v2024-11-05; broader product impact is not established in the bundle.
Likely exposure
Exposure appears limited to Google MCP Toolbox for Databases users connecting via Toolbox using SSE under MCP specification v2024-11-05. The affected-version data is sparse and lists version 0 with default status unaffected, so teams should validate actual installed versions and connection mode against Google guidance.
Exploitation context
The CVE is not listed as KEV in the provided bundle, and no cited source claims active exploitation. The CVSS vector indicates network attackability, low complexity, no privileges, and required user interaction. DNS rebinding risk is most relevant where a user browser can reach an affected local or internal Toolbox endpoint.
Researcher notes
Evidence is limited to the CVE text, CVSS, CWE-942, and linked GitHub issue/PR references. The bundle does not provide exploit details, affected release ranges beyond version 0, a named fixed version, or proof of exploitation. Validation should focus on transport mode, CORS behavior, host/origin enforcement, and vendor release status.
Mitigation direction
- Check Google issue and pull request guidance for fixed versions or configuration changes.
- Identify and prioritize Toolbox deployments using SSE with MCP spec v2024-11-05.
- Disable or restrict SSE access until vendor-confirmed remediation is applied.
- Ensure SSE responses do not allow wildcard origins where origin restrictions are expected.
- Limit Toolbox network reachability to trusted interfaces, users, and networks.
- Review allowed-origins and allowed-hosts settings for intended enforcement.
Validation and detection
- Inventory MCP Toolbox instances, versions, and enabled connection transports.
- Confirm whether any deployment uses SSE under MCP specification v2024-11-05.
- Review SSE initialization behavior for wildcard CORS exposure.
- Verify allowed-origins and allowed-hosts controls are actually enforced.
- Check vendor references for remediation status before closing risk.
- Monitor for any later KEV or vendor exploitation updates.
Public sources used
Based on public source material and reviewed before publication.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-942: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2026-9739 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Critical
- CVSS
- 9.4 (4.0)
- Known Exploited
- No
- Published
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H — — Google Vulnerability scoring details
Base CVSS 4.0 score
9.4 CriticalVector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reserved CVE Program
The CVE ID was reserved by the assigning CNA.
- CVE published CVE Program
The CVE record was published.
- CVE updated CVE Program
The CVE record metadata indicates this as the latest update time.
Source materials
- CVE List V5 source CVE List V5
- https://github.com/googleapis/mcp-toolbox/issues/3053 CVE reference, Google
- https://github.com/googleapis/mcp-toolbox/pull/3054 CVE reference, Google
Products and packages named in the record
CWE details
CWE links open conservative ATT&CK lookup hints, not official CWE-to-ATT&CK mappings. Source links are consolidated once in the official source material section above.