CVE-2026-34742: The Go MCP SDK used Go's standard encoding/json

Q: How do I fix CVE-2026-34742?

mcp go sdk: upgrade to 1.4.0. Exact commands for each OS are on this page.

Q: Is CVE-2026-34742 being exploited?

CVE-2026-34742 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-34742 affect?

CVE-2026-34742 affects mcp go sdk. Severity is high (CVSS 8.1). 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 w

Routine

HIGH 8.1UPGRADE

CVE-2026-34742 is a high-severity flaw (CVSS 8.1) affecting mcp go sdk. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 al

Why this priority

High severity

A fixed release or distro patch exists.

Risk facts

CVSS score	8.1 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.5% (top 61%)
CISA exploited list	No
Weakness	CWE-1188
Published	2026-04-02
Last modified	2026-07-24

Publisher (CNA): GitHub, Inc. · Vendor: lfprojects

Last updated 2026-07-24 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-02 19:21 UTCPublished CVE record published
2026-07-24 21:10 UTCUpdated Record last modified

lfprojects mcp go sdk UPGRADE

Affected: < 1.4.0

Fixed in: 1.4.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy mcp-go-sdk || rpm -q mcp-go-sdk || mcp-go-sdk --version

2. UPGRADE to 1.4.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade mcp-go-sdk

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade mcp-go-sdk

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-34742?

mcp go sdk: upgrade to 1.4.0. Exact commands for each OS are on this page.

Is CVE-2026-34742 being exploited?

CVE-2026-34742 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-34742 affect?

CVE-2026-34742 affects mcp go sdk. Severity is high (CVSS 8.1). 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 w

How urgent is CVE-2026-34742?

Priority 38/100. High severity

References

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