CVE-2026-9739

Published: Mag 28, 2026 Last Modified: Mag 28, 2026
ExploitDB:
Other exploit source:
Google Dorks:
CRITICAL 9,4
Source: [email protected]
Attack Vector: network
Attack Complexity: low
Privileges Required: none
User Interaction: active
Confidentiality: N/A
Integrity: N/A
Availability: N/A

Description

AI Translation Available

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.

942

Permissive Cross-domain Security Policy with Untrusted Domains

Incomplete
Abstraction: Variant Structure: Simple
Common Consequences
Security Scopes Affected:
Confidentiality Integrity Availability Access Control
Potential Impacts:
Execute Unauthorized Code Or Commands Bypass Protection Mechanism Read Application Data Varies By Context
Applicable Platforms
Technologies: Web Based, Web Server
View CWE Details
https://github.com/googleapis/mcp-toolbox/issues/3053
https://github.com/googleapis/mcp-toolbox/issues/3053
https://github.com/googleapis/mcp-toolbox/pull/3054
https://github.com/googleapis/mcp-toolbox/pull/3054