CVE-2026-34742

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.

Database specific

{
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/34xxx/CVE-2026-34742.json",
    "cwe_ids": [
        "CWE-1188"
    ],
    "cna_assigner": "GitHub_M"
}

References

Affected packages

Git / github.com/modelcontextprotocol/go-sdk

Affected ranges

Type: GIT
Repo: https://github.com/modelcontextprotocol/go-sdk
Events: Introduced

0 Unknown introduced commit / All previous commits are affected

Fixed

c9317fb5b75328ca2faeaf8ea0e23a53c37de49f

Affected versions

v0.*

v0.1.0

v0.2.0

v0.3.0

v0.3.1

v0.4.0

v0.5.0

v0.6.0

v0.7.0

v0.8.0

v1.*

v1.0.0

v1.1.0

v1.1.0-pre.1

v1.1.0-pre.2

v1.2.0

v1.2.0-pre.1

v1.2.0-pre.2

v1.3.0

v1.3.0-pre.1

Database specific

source

"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-34742.json"