October 6, 2026

CVE Watchtower

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CVE-2026-9739NVD

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: Unknown/Unlisted Weakness ↗
Refer to the official MITRE database for detailed architectural specifications regarding this weakness.
CVSS v4.0 Base Metrics — Score 9.4
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
Not provided by Private for this CVE.
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🎁7-Day Free Trial — Try Pro or Team, no card required.
📧Email Delivery — Threat intel straight to your inbox.
♾️Unlimited Vendors — Track your entire stack.
🚨All New CVEs — Be the first to know.
📈EPSS Spike Alerts — Catch rising risk before it peaks.
🎯Custom EPSS/CVSS — Filter noise, focus on risk.
🛡️Exploit Intel — A 2nd confirmed-exploit signal beyond KEV.
🐙GitHub Issues — Auto-tracked, no duplicates.
📬Weekly Digest — One clean summary, not inbox spam.
🏷️Watchlist Groups — Tag alerts by team (Infra/AppSec/SOC).
💬Webhooks — Slack & Teams integration.
🔀Smart Routing — Critical alerts to one channel, rest to another.
🚫Ad-Free — Uninterrupted experience.

External References