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Fencer Vulns
high 7.1

CVE-2026-33252 json

MCP Go SDK Allows Cross-Site Tool Execution for HTTP Servers without Authorizatrion

published 2026-03-19 7 mo ago modified 2026-09-10 1 mo ago also EUVD-2026-14643 , GHSA-89xv-2j6f-qhc8 , GO-2026-4773

cvss
7.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 7%
public exploits
0
none known

Summary

The Go MCP SDK used Go's standard encoding/json. Prior to version 1.4.1, the Go SDK's Streamable HTTP transport accepted browser-generated cross-site `POST` requests without validating the `Origin` header and without requiring `Content-Type: application/json`. In deployments without Authorization, especially stateless or sessionless configurations, this allows an arbitrary website to send MCP requests to a local server and potentially trigger tool execution. Version 1.4.1 contains a patch for the issue.

Patch / fix

  • go github.com/modelcontextprotocol/go-sdk 1.4.1
  • lfprojects mcp_go_sdk 1.4.1
  • govulncheck-vulndb openSUSE Leap 15.6 0.0.20260326T203309-150000.1.155.2

suse advisories SUSE-SU-2026:1135-1

  • 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-2026-33252 updated cvss 7.1

encoding/json: golang: github.com/modelcontextprotocol/go-sdk: Go MCP SDK: Remote tool execution via cross-site request forgery

  • 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-clients, openshift-serverless-1/kn-client-kn-rhel9, openshift-serverless-1/kn-plugin-func-func-util-rhel9 Red Hat OpenShift AI (RHOAI) rhoai/odh-mod-arch-gen-ai-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
    not affected: vulnerable code not present
  • Red Hat Hardened Images golang1.25, golang1.26
    not affected: component not present
  • 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
partial
Assessed
7 mo ago

Exploit prediction

0.18% chance of exploitation in the next 30 days, higher than 7% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:L
GitHub 3.1 7.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:L
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

Affected packages

ecosystem package affected fixed in
go github.com/modelcontextprotocol/go-sdk
<1.4.1
1.4.1

Affected products

  • modelcontextprotocol go-sdk

Classification

Weakness
  • CWE-352 Cross-Site Request Forgery

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.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.