CVE-2026-34742CWE-1188

Model Context Protocol Go SDK: DNS Rebinding Protection Disabled by Default for Servers Running on Localhost

High · published April 2, 2026

CVSS v4.0
7.6
EPSS
1%
Percentile
51.1
In the wild
Unconfirmed
What it is

The Go MCP SDK used Go's standard encoding/json. Prior to version 1.4.0, 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. This issue has been patched in version 1.4.0.

The record
Technical detail
CVSS v4.0
7.6 · HIGH
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
EPSS
0.00664 · 51.1th percentile
Weakness
CWE-1188 · Initialization of a Resource with an Insecure Default
Published
2026-04-02T18:32Z
EPSS history
Timeline
  • 02 APR 18:32Z
    Model Context Protocol Go SDK: DNS Rebinding Protection Disabled by Default for Servers Running on Localhost
    cvelistv5