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CVE-2026-34742 Details

Description

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.

Metrics

CVSS 3.x Severity and Vector Strings:

NIST: [email protected]CVSS-B:8.1 HIGHVector:CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

CNA: redhat-SADPCVSS-B:8 HIGHVector:CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N

References to Advisories, Solutions, and Tools

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URL	Source(s)	Tag(s)
https://access.redhat.com/errata/RHSA-2026:21772	redhat-SADP
https://access.redhat.com/security/cve/CVE-2026-34742	redhat-SADP
https://bugzilla.redhat.com/show_bug.cgi?id=2454608	redhat-SADP
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-34742.json	redhat-SADP
https://github.com/modelcontextprotocol/go-sdk/commit/67bd3f2e2b53ce11a16db8d976cdb8ff1e986b6d	[email protected]	Patch
https://github.com/modelcontextprotocol/go-sdk/pull/760	[email protected]	Issue TrackingPatch
https://github.com/modelcontextprotocol/go-sdk/releases/tag/v1.4.0	[email protected]	Release Notes
https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-xw59-hvm2-8pj6	[email protected]	Vendor Advisory

see all 8 references

Weakness Enumeration

CWE-ID	CWE Name	Source
CWE-1188	Initialization of a Resource with an Insecure Default	redhat-SADP
CWE-1188	Initialization of a Resource with an Insecure Default	[email protected]

Affected Products

Product	Versions
lfprojects mcp go sdk	< 1.4.0
CPE cpe:2.3:a:lfprojects:mcp_go_sdk:::::::: Remediation No remediation found in references.

Change History

7 change records found show changes

Date	Action	Recorded By
Jul 24, 2026	CVE Translated	[email protected]
Jul 15, 2026	CVE Modified	redhat-SADP
Jun 30, 2026	CVE Modified	redhat-SADP
Jun 17, 2026	CVE Modified	CISA-ADP
Jun 17, 2026	CVE Modified	[email protected]
Apr 3, 2026	Initial Analysis	[email protected]
Apr 2, 2026	New CVE Received	[email protected]