GHSA-hv2w-8mjj-jw22
MEDIUMGHSA-hv2w-8mjj-jw22 is a medium-severity (CVSS 6.1) CWE-942 vulnerability in io.modelcontextprotocol.sdk:mcp-core. O3 Security confirms whether GHSA-hv2w-8mjj-jw22 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
MCP Java SDK has a Hardcoded Wildcard CORS (Access-Control-Allow-Origin: *)
Blast Radius
io.modelcontextprotocol.sdk:mcp-core☕io.modelcontextprotocol.sdk:mcp-core☕io.modelcontextprotocol.sdk:mcp-coreReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
Summary
Hardcoded Wildcard CORS (Access-Control-Allow-Origin: * )
- 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
Attack Scenario
An attacker-controlled web page instructs the victim's browser to open GET https://internal-mcp-server/sse. Because Access-Control-Allow-Origin: * allows cross-origin SSE reads, the attacker's page receives the endpoint event — which contains the session ID. The attacker can then POST to that endpoint from their page using the victim's browser as a relay.
Comparison with python-sdk
No Access-Control-Allow-Origin header is emitted by either Python transport. The browser's default same-origin policy remains in full effect. https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/sse.py https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/streamable_http.py
Recommendation
In the SDK, the transport layer should not own CORS policy. Server implementors who need cross-origin access can add a CORS filter at the servlet filter or Spring Security layer.
Reference
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.modelcontextprotocol.sdk:mcp-core | ≥ 1.0.0&&< 1.0.1 | 1.0.1 |
| ☕Maven | io.modelcontextprotocol.sdk:mcp-core | ≥ 1.1.0&&< 1.1.1 | 1.1.1 |
| ☕Maven | io.modelcontextprotocol.sdk:mcp-core | all versions | 0.18.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for io.modelcontextprotocol.sdk:mcp-core. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update io.modelcontextprotocol.sdk:mcp-core to 1.0.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-hv2w-8mjj-jw22 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-hv2w-8mjj-jw22 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-hv2w-8mjj-jw22. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-hv2w-8mjj-jw22 in your dependencies?
O3 detects GHSA-hv2w-8mjj-jw22 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.