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.
- 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
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
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 | 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 include 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
Sources
Also known as GHSA-hv2w-8mjj-jw22.