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HIGH

CVE-2026-63127

CVSS v3

8.2

HIGH

EPSS Score

0.2 %

exploit probability, as of 2026-09-29

CISA KEV

No

known exploited

Exploitation

—

SSVC status

Description

RMCP is an official Rust SDK for the Model Context Protocol. Prior to 2.0.0, the rmcp crate's OAuth implementation in crates/rmcp/src/transport/auth.rs omits the RFC 9728 resource field from ResourceServerMetadata and allows discover_oauth_server_via_resource_metadata to use protected-resource metadata without confirming that the returned resource identifier exactly matches the configured MCP server. A malicious MCP server can publish metadata for a different legitimate MCP resource and its auth

Technical details

Published
2026-09-16
Last Modified
2026-09-16

Frequently asked questions

What is CVE-2026-63127?

RMCP is an official Rust SDK for the Model Context Protocol. Prior to 2.0.0, the rmcp crate's OAuth implementation in crates/rmcp/src/transport/auth.rs omits the RFC 9728 resource field from ResourceServerMetadata and allows discover_oauth_server_via_resource_metadata to use protected-resource metadata without confirming that the returned resource identifier exactly matches the configured MCP server. A malicious MCP server can publish metadata for a different legitimate MCP resource and its auth

Is CVE-2026-63127 actively exploited?

Active exploitation of CVE-2026-63127 has not been confirmed. Its EPSS score was 0.2% on 2026-09-29, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-63127?

CVE-2026-63127 has a CVSS v3 base score of 8.2 (HIGH severity).

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