Bug 2535526

Summary: CVE-2026-63127 goose: RMCP: Token impersonation via missing OAuth resource field validation [epel-all]
Product: [Fedora] Fedora EPEL Reporter: Samuele Negrini <snegrini>
Component: gooseAssignee: RHEL Lightspeed Maint <rhel-lightspeed>
Status: CLOSED CURRENTRELEASE QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: epel10CC: jkonecny, rhel-lightspeed, rodolfo.olivieri3, rust-sig
Target Milestone: ---Keywords: Security, SecurityTracking
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard: {"flaws": ["c5e4f491-e66f-4565-b1d8-24355ea851b0"]}
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Last Closed: 2026-10-15 09:29:22 UTC Type: ---
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Bug Depends On:    
Bug Blocks: 2535503    

Description Samuele Negrini 2026-09-16 16:02:01 UTC 
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.

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 authorization server, causing a victim who connects and completes the authorization flow to obtain a legitimate access token that the client subsequently sends to the malicious server. The attacker can capture the token and impersonate the victim against the legitimate MCP resource within the token's granted scopes. This issue is fixed in version 2.0.0.
Comment 1 Jiri Konecny 2026-10-15 09:29:22 UTC 
Fixed by latest 1.45 Goose update.