# CVE-2026-33252: MCP Go SDK Allows Cross-Site Tool Execution for HTTP Servers without Authorizatrion

> An attacker can force a victim's browser to execute tools on a local MCP server by bypassing origin checks in the Go SDK's HTTP transport.

- **Severity:** High 7.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 23 Mar 2026
- **Updated:** 24 Mar 2026
- **Also known as:** CLEANSTART-2026-RU81320, CLEANSTART-2026-YF18656, GHSA-89xv-2j6f-qhc8, GO-2026-4773, MINI-3xjf-pmwg-9r77, MINI-95p6-8pr9-2cc7, MINI-fvgq-795f-cq8f, MINI-h24m-qh9m-m6xj

## What is CVE-2026-33252?

CVE-2026-33252 is a high-severity vulnerability in modelcontextprotocol go-sdk, published on 23 Mar 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

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 tool execution. Version 1.4.1 contains a patch for the issue.

Weakness: CWE-352 (Cross-Site Request Forgery)

## Which versions are affected by CVE-2026-33252?

3 open source packages ship an affected version, including github.com/modelcontextprotocol/go-sdk. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/modelcontextprotocol/go-sdk` | Go | All versions | 1.4.1 |
| `github.com/modelcontextprotocol/go-sdk` | Go | All versions | 1.4.1 |
| `github.com/modelcontextprotocol/go-sdk` | Go | All versions | 1.4.1 |

Products: Lfprojects Mcp Go Sdk.

## How do I fix CVE-2026-33252?

Upgrade github.com/modelcontextprotocol/go-sdk to 1.4.1 or later.

## Is CVE-2026-33252 being exploited?

There is no known exploitation of CVE-2026-33252 in the wild and no public exploit code.

## Other vulnerabilities in modelcontextprotocol go-sdk

- [CVE-2026-34742](https://insights.sbomify.com/CVE-2026-34742/): Model Context Protocol Go SDK: DNS Rebinding Protection Disabled by Default for Servers Running on Localhost (high 7.6)
- [CVE-2026-27896](https://insights.sbomify.com/CVE-2026-27896/): MCP Go SDK Vulnerable to Improper Handling of Case Sensitivity (high 7.0)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-33252 and fix it if it is affected.

What it is: CVE-2026-33252 is a high-severity vulnerability in modelcontextprotocol go-sdk, published on 23 Mar 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-33252 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/modelcontextprotocol/go-sdk (Go): affected all versions; fixed in 1.4.1
- github.com/modelcontextprotocol/go-sdk (Go): affected all versions; fixed in 1.4.1
- github.com/modelcontextprotocol/go-sdk (Go): affected all versions; fixed in 1.4.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-33252/ (Markdown: https://insights.sbomify.com/CVE-2026-33252/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-33252
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-33252
- OSV: https://osv.dev/vulnerability/CVE-2026-33252

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-33252/
Summaries are generated and may contain mistakes; the official description above is the record.