# CVE-2026-34237: MCP Java SDK has a Hardcoded Wildcard CORS (Access-Control-Allow-Origin: *)

> The MCP Java SDK uses a hardcoded wildcard CORS policy, allowing any origin to access resources, which attackers can exploit to bypass same-origin restrictions.

- **Severity:** Medium 6.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N`)
- **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:** 31 Mar 2026
- **Updated:** 9 Jun 2026
- **Also known as:** GHSA-hv2w-8mjj-jw22

## What is CVE-2026-34237?

CVE-2026-34237 is a medium-severity vulnerability in modelcontextprotocol java-sdk, published on 31 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

MCP Java SDK is the official Java SDK for Model Context Protocol servers and clients. Prior to versions 0.83.0, 1.0.1, and 1.1.1, there is a hardcoded wildcard CORS vulnerability. This issue has been patched in versions 0.83.0, 1.0.1, and 1.1.1.

Weakness: CWE-942 (Permissive Cross-domain Security Policy with Untrusted Domains)

## Which versions are affected by CVE-2026-34237?

6 open source packages ship an affected version, including io.modelcontextprotocol.sdk:mcp-core. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `io.modelcontextprotocol.sdk:mcp-core` | Maven | All versions | 0.18.3 |
| `io.modelcontextprotocol.sdk:mcp-core` | Maven | All versions | 0.18.3 |
| `io.modelcontextprotocol.sdk:mcp-core` | Maven | From 1.0.0 | 1.0.1 |
| `io.modelcontextprotocol.sdk:mcp-core` | Maven | From 1.0.0 | 1.0.1 |
| `io.modelcontextprotocol.sdk:mcp-core` | Maven | From 1.1.0 | 1.1.1 |
| `io.modelcontextprotocol.sdk:mcp-core` | Maven | From 1.1.0 | 1.1.1 |

Products: Lfprojects Mcp Java Sdk.

## How do I fix CVE-2026-34237?

Upgrade io.modelcontextprotocol.sdk:mcp-core to a fixed version for your release line: 0.18.3, 1.0.1 or 1.1.1.

## Is CVE-2026-34237 being exploited?

There is no known exploitation of CVE-2026-34237 in the wild and no public exploit code.

## Other vulnerabilities in modelcontextprotocol java-sdk

- [CVE-2026-35568](https://insights.sbomify.com/CVE-2026-35568/): MCP Java-SDK has a DNS Rebinding Vulnerability (high 7.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-34237 and fix it if it is affected.

What it is: CVE-2026-34237 is a medium-severity vulnerability in modelcontextprotocol java-sdk, published on 31 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-2026-34237 in the wild and no public exploit code.

Affected packages and fixed versions:
- io.modelcontextprotocol.sdk:mcp-core (Maven): affected all versions; fixed in 0.18.3
- io.modelcontextprotocol.sdk:mcp-core (Maven): affected all versions; fixed in 0.18.3
- io.modelcontextprotocol.sdk:mcp-core (Maven): affected from 1.0.0; fixed in 1.0.1
- io.modelcontextprotocol.sdk:mcp-core (Maven): affected from 1.0.0; fixed in 1.0.1
- io.modelcontextprotocol.sdk:mcp-core (Maven): affected from 1.1.0; fixed in 1.1.1
- io.modelcontextprotocol.sdk:mcp-core (Maven): affected from 1.1.0; fixed in 1.1.1

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-2026-34237/ (Markdown: https://insights.sbomify.com/CVE-2026-34237/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-34237
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-34237
- OSV: https://osv.dev/vulnerability/CVE-2026-34237

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-34237/
Summaries are generated and may contain mistakes; the official description above is the record.