Skip to content
Fencer Vulns
high 8.0

CVE-2026-34742 json

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

published 2026-04-01 7 mo ago modified 2026-07-24 3 mo ago also GHSA-xw59-hvm2-8pj6 , GO-2026-5771 , EUVD-2026-18503

cvss
8.0
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 41%
public exploits
0
none known

Summary

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.

Patch / fix

  • go github.com/modelcontextprotocol/go-sdk 1.4.0
  • Red Hat Red Hat OpenShift Dev Spaces 3.28 1779829736
  • govulncheck-vulndb openSUSE Leap 16.0 0.0.20260723T184607-160000.1.1

opensuse advisories openSUSE-SU-2026:21483-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-34742 updated cvss 8.0

github.com/modelcontextprotocol/go-sdk: Model Context Protocol (MCP) Go SDK: DNS rebinding vulnerability allows unauthorized access

  • Red Hat Migration Toolkit for Virtualization mtv-candidate/mtv-api-rhel9, mtv-candidate/mtv-operator-bundle, mtv-candidate/mtv-controller-rhel9, mtv-candidate/mtv-cli-download-rhel9, migration-toolkit-virtualization/mtv-cli-download-rhel9
    affected: workaround, no fix planned “Will not fix”
  • Red Hat OpenShift Serverless openshift-serverless-1/kn-client-kn-rhel9, openshift-serverless-1/kn-plugin-func-func-util-rhel9
    affected: workaround, no fix available
  • Red Hat OpenShift Dev Spaces 3.28 devspaces/udi-rhel9 1779829736
    fixed: vendor fix RHSA-2026:21772
  • Red Hat OpenShift Lightspeed openshift-lightspeed/openshift-mcp-server-rhel9 Red Hat OpenShift AI (RHOAI) rhoai/odh-mod-arch-gen-ai-rhel9 Red Hat OpenShift Dev Spaces 3.28 devspaces/code-rhel9 1779814592, devspaces/server-rhel9 1779342423, devspaces/openvsx-rhel9 1779528224, devspaces/traefik-rhel9 1779786779, devspaces/udi-base-rhel9 1779741066, devspaces/code-sshd-rhel9 1779813519, +9 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
7 mo ago

Exploit prediction

0.47% chance of exploitation in the next 30 days, higher than 41% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 4.0 7.6 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
CISA ADP 3.1 8.0 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N
CNA 4.0 7.6 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
NVD 3.1 8.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
CNA 3.1 8.0 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N
GitHub 3.1 8.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

Affected packages

ecosystem package affected fixed in
go github.com/modelcontextprotocol/go-sdk
<1.4.0
1.4.0

Affected products

  • modelcontextprotocol go-sdk
  • Red Hat Red Hat OpenShift Dev Spaces 3.28
  • Red Hat Migration Toolkit for Virtualization
  • Red Hat OpenShift Lightspeed
  • Red Hat OpenShift Serverless
  • Red Hat Red Hat OpenShift AI (RHOAI)

Classification

Weakness
  • CWE-1188 Initialization of a Resource with an Insecure Default

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.