CVE-2026-9739

May 27, 2026, 11:16 p.m.

9.4
Critical

Description

Vulnerable to DNS rebinding attacks when using SSE (http://b/499408790). During the beta phase, we implemented `allowed-origins` and `allowed-hosts` flags to align with MCP security guidelines. However, the hardcoded `Access-Control-Allow-Origin: *` header in the SSE initialization handler was inadvertently retained. This vulnerability specifically impacts users connecting via Toolbox using SSE under specification v2024-11-05.

Product(s) Impacted

Vendor Product Versions
Google
  • Toolbox
  • Sse
  • *
  • *

Weaknesses

Common security weaknesses mapped to this vulnerability.

CWE-942
Permissive Cross-domain Policy with Untrusted Domains
The product uses a cross-domain policy file that includes domains that should not be trusted.

*CPE(s)

Affected systems and software identified for this CVE.

Type Vendor Product Version Update Edition Language Software Edition Target Software Target Hardware Other Information
a google toolbox / / / / / / / *
a google sse / / / / / / / *

References

https://github.com/googleapis/mcp-toolbox/issues/3053
https://github.com/googleapis/mcp-toolbox/pull/3054

Tags

[email protected]
CWE-942
2026-05-27
CVE-2026-9739

CVSS Score

9.4 / 10

CVSS Data - 4.0

  • Attack Vector: NETWORK
  • Attack Complexity: LOW
  • Attack Requirements: NONE
  • Privileges Required: NONE
  • User Interaction: ACTIVE
  • Scope:
  • Confidentiality Impact: HIGH
  • Integrity Impact: HIGH
  • Availability Impact: HIGH
  • Exploit Maturity: NOT_DEFINED

    • 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

    View Vector String

Timeline

Published: May 27, 2026, 11:16 p.m.
Last Modified: May 27, 2026, 11:16 p.m.

Status : Received

CVE has been recently published to the CVE List and has been received by the NVD.

More info

Source

[email protected]

*Disclaimer: Some vulnerabilities do not have an associated CPE. To enhance the data, we use AI to infer CPEs based on CVE details. This is an automated process and might not always be accurate.