How severe is CVE-2026-34742?

CVE-2026-34742 has a CVSS 3.x base score of 8.1, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability none.

Is CVE-2026-34742 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (36th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-34742?

CVE-2026-34742 affects Lfprojects Mcp Go Sdk. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-34742?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-34742 have an EU (EUVD) identifier?

Yes. CVE-2026-34742 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-18503.

When was CVE-2026-34742 published?

CVE-2026-34742 was published on 2026-04-02 and last updated on 2026-06-30.

CVE-2026-34742

CVE-2026-34742 is a high-severity vulnerability in Lfprojects Mcp Go Sdk with a CVSS 3.x base score of 8.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-1188.

Key facts

Severity: High (CVSS 3.x base score 8.1)
CVSS v4: 7.6
EPSS exploit prediction: 0% (36th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-18503
Weakness: CWE-1188
Affected product: Lfprojects Mcp Go Sdk
Published: 2026-04-02
Last modified: 2026-06-30

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.

Frequently asked questions

What is 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.
How severe is CVE-2026-34742?: CVE-2026-34742 has a CVSS 3.x base score of 8.1, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2026-34742 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (36th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-34742?: CVE-2026-34742 affects Lfprojects Mcp Go Sdk. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-34742?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-34742 have an EU (EUVD) identifier?: Yes. CVE-2026-34742 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-18503.
When was CVE-2026-34742 published?: CVE-2026-34742 was published on 2026-04-02 and last updated on 2026-06-30.

References

Affected products (1)

cpe:2.3:a:lfprojects:mcp_go_sdk:*:*:*:*:*:*:*:*

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