CVE-2026-33252: The Go MCP SDK used Go's standard encoding/json

Q: How do I fix CVE-2026-33252?

mcp go sdk: upgrade to 1.4.1. Exact commands for each OS are on this page.

Q: Is CVE-2026-33252 being exploited?

CVE-2026-33252 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-2026-33252 affect?

CVE-2026-33252 affects mcp go sdk. Severity is high (CVSS 7.1). 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

Routine

HIGH 7.1UPGRADE

CVE-2026-33252 is a high-severity flaw (CVSS 7.1) 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 1.4.1, 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 too

Why this priority

High severity

A fixed release or distro patch exists.

Risk facts

CVSS score	7.1 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.2% (top 92%)
CISA exploited list	No
Weakness	CWE-352
Published	2026-03-24
Last modified	2026-06-17

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

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-03-24 00:16 UTCPublished CVE record published
2026-06-17 10:37 UTCUpdated Record last modified

lfprojects mcp go sdk UPGRADE

Affected: < 1.4.1

Fixed in: 1.4.1

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 1.4.1 (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-2026-33252?

mcp go sdk: upgrade to 1.4.1. Exact commands for each OS are on this page.

Is CVE-2026-33252 being exploited?

CVE-2026-33252 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-2026-33252 affect?

CVE-2026-33252 affects mcp go sdk. Severity is high (CVSS 7.1). 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

How urgent is CVE-2026-33252?

Priority 27/100. High severity

Related CVEs

CVE-2026-34742 HIGH 8.1 UPGRADE The Go MCP SDK used Go's standard encoding/json
CVE-2026-27896 HIGH 7.5 UPGRADE The Go MCP SDK used Go's standard encoding/json.Unmarshal for JSON-RPC and MCP protocol message parsing in ver

References

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