CVE-2026-9739
Published:May 27, 2026
Updated:June 13, 2026
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.
Affected Packages
https://github.com/googleapis/mcp-toolbox.git (GITHUB):
Affected version(s) >=v0.0.1 <v1.2.0Fix Suggestion:
Update to version v1.2.0github.com/googleapis/mcp-toolbox (GO):
Affected version(s) >=v0.0.0-20260521214943-b0010060a939 <v1.2.0Fix Suggestion:
Update to version v1.2.0Related Resources (2)
Do you need more information?
Contact UsCVSS v4
Base Score:
9.4
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
NONE
User Interaction
ACTIVE
Vulnerable System Confidentiality
HIGH
Vulnerable System Integrity
HIGH
Vulnerable System Availability
HIGH
Subsequent System Confidentiality
HIGH
Subsequent System Integrity
HIGH
Subsequent System Availability
HIGH
CVSS v3
Base Score:
9.6
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
REQUIRED
Scope
CHANGED
Confidentiality
HIGH
Integrity
HIGH
Availability
HIGH
Weakness Type (CWE)
Permissive Cross-domain Security Policy with Untrusted Domains
EPSS
Base Score:
0.02