CVE-2026-34742

HIGH
2026-04-01 https://github.com/modelcontextprotocol/go-sdk GHSA-xw59-hvm2-8pj6
7.6
CVSS 4.0
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CVSS Vector

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/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
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
P
Scope
X

Lifecycle Timeline

3
Patch Released
Apr 02, 2026 - 02:30 nvd
Patch available
Analysis Generated
Apr 01, 2026 - 21:15 vuln.today
CVE Published
Apr 01, 2026 - 21:09 nvd
HIGH 7.6

Tags

Authentication Bypass

Description

The Model Context Protocol (MCP) Go SDK does not enable DNS rebinding protection by default for HTTP-based servers. When an HTTP-based MCP server is run on localhost without authentication with `StreamableHTTPHandler` or `SSEHandler`, a malicious website could exploit DNS rebinding to bypass same-origin policy restrictions and send requests to the local MCP server. This could allow an attacker to invoke tools or access resources exposed by the MCP server on behalf of the user in those limited circumstances. Note that running HTTP-based MCP servers locally without authentication is not recommended per MCP security best practices. This issue does not affect servers using stdio transport. Servers created via `StreamableHTTPHandler` or `SSEHandler` now have this protection enabled by default when binding to `localhost`. Users are advised to update to version `1.4.0` to receive this automatic protection.

Analysis

DNS rebinding attacks can bypass same-origin policy in Model Context Protocol (MCP) Go SDK versions prior to 1.4.0, enabling malicious websites to send unauthorized requests to localhost HTTP servers. Affects servers using StreamableHTTPHandler or SSEHandler when run without authentication on localhost. …

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Remediation

Within 24 hours: Identify all internal applications and services using MCP Go SDK and document current versions deployed. Within 7 days: For production systems, enforce authentication on all StreamableHTTPHandler and SSEHandler endpoints and restrict localhost access to trusted networks only. …

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Priority Score

38
Low Medium High Critical
KEV: 0
EPSS: +0.1
CVSS: +38
POC: 0

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CVE-2026-34742 vulnerability details – vuln.today
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