Origin Validation Error Affecting io.modelcontextprotocol.sdk:mcp-core package, versions [,0.18.0)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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- published8 Apr 2026
- disclosed7 Apr 2026
- creditJonathan Leitschuh
Introduced: 7 Apr 2026
CVE-2026-35568 (opens in a new tab)How to fix?
Upgrade io.modelcontextprotocol.sdk:mcp-core to version 0.18.0 or higher.
Overview
Affected versions of this package are vulnerable to Origin Validation Error through the lack CORS checks (Host and Origin header validation) on incoming HTTP connections. An attacker can gain unauthorized access to local or private-network servers by tricking a victim into visiting a malicious website, which then issues requests to the server as if originating from a trusted source.
Workaround
This vulnerability can be mitigated by running the server behind a reverse proxy (such as Nginx or HAProxy) configured to strictly validate the Host and Origin headers, or by using a framework that enforces strict CORS and Origin validation.