November 14, 2026

CVE Watchtower

CVE-2026-9739github.com/googleapis/mcp-toolbox

NVD

Vulnerability Summary

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.
Severity Level
CRITICAL
Published Date
May 27, 2026
Last Modified
Jul 1, 2026
Exploitation Status
No confirmed exploitation yet
CVE Record Status
Published
EPSS Score (30-Day)
0.28%Probability
Root Weakness (CWE)
CWE-942 β†—
See the MITRE CWE entry for the full definition of this weakness.
CVSS v4.0 Base Metrics — Score 9.4
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
Attack VectorNetwork
Attack ComplexityLow
Attack RequirementsNone
Privileges RequiredNone
User InteractionActive
Confidentiality (Vulnerable System)High
Integrity (Vulnerable System)High
Availability (Vulnerable System)High
Confidentiality (Subsequent System)High
Integrity (Subsequent System)High
Availability (Subsequent System)High

Affected & Patched Versions

Affected Versions
  • github.com/googleapis/mcp-toolbox < 1.2.0
Patched Versions
No patched version published yet
Until a fix ships, reduce exposure:
  • Restrict access to the affected service or interface to trusted networks.
  • Disable the affected feature if you do not need it.
  • Watch the vendor advisory for a firmware or software update.

What to do

Plan remediation soon. No exploitation is confirmed yet, but the severity is critical.

  1. Check whether you run github.com/googleapis/mcp-toolbox and which version.
  2. No patched version is listed yet. Limit access to the affected service to trusted networks, and disable the feature if you can.
  3. Subscribe to the vendor advisory so you learn when a fix ships.

Timeline

  • May 27, 2026Published
  • Jul 1, 2026Record last modified

Score, severity and exploitation changes are tracked from the day Watchtower started logging them.

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Related Coverage

External References

Data last checked: Sep 23, 2026 13:57 UTC