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

Severity: medium (CVSS 6.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-03-31 · updated 2026-07-24
Weakness: CWE-942

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.

Affected products

modelcontextprotocol java-sdk: before 1.0.1; 1.1.0 — fixed in 1.0.1

How to fix

Upgrade to a fixed version: modelcontextprotocol java-sdk 1.0.1. Check the vendor advisory for mitigations.

References

https://github.com/modelcontextprotocol/java-sdk/blob/main/mcp-core/src/main/java/io/modelcontextprotocol/server/transport/HttpServletSseServerTransportProvider.java#L289
https://github.com/modelcontextprotocol/java-sdk/blob/main/mcp-core/src/main/java/io/modelcontextprotocol/server/transport/HttpServletStreamableServerTransportProvider.java#L525
https://github.com/modelcontextprotocol/java-sdk/security/advisories/GHSA-hv2w-8mjj-jw22

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