https://vulnerability.circl.lu/sightings/feed 2026-09-19T15:44:44.934593+00:00 Vulnerability-Lookup info@circl.lu python-feedgen Contains only the most 10 recent sightings. https://vulnerability.circl.lu/sighting/fb2cf0fd-65cc-4994-af32-f3b74a972b3c/export 2026-09-19T15:44:44.941904+00:00 Automation user https://vulnerability.circl.lu/user/automation {"uuid": "fb2cf0fd-65cc-4994-af32-f3b74a972b3c", "vulnerability_lookup_origin": "1a89b78e-f703-45f3-bb86-59eb712668bd", "author": "9f56dd64-161d-43a6-b9c3-555944290a09", "vulnerability": "GHSA-33f5-2c5q-wgwj", "type": "seen", "source": "https://gist.github.com/alon710/16597bd55d59e6c89394c487c227381c", "content": "# CVE-2026-63127: CVE-2026-63127: OAuth Resource Spoofing and Token Leakage in rmcp SDK\n\n> **CVSS Score:** 8.2\n> **Published:** 2026-09-16\n> **Full Report:** https://cvereports.com/reports/CVE-2026-63127\n\n## Summary\nAn OAuth resource spoofing vulnerability in the rmcp crate prior to 2.0.0 allows a malicious Model Context Protocol (MCP) server to spoof protected resource metadata. By presenting metadata pointing to a legitimate resource and authorization server, the attacker can trick the client into completing the authentication flow and subsequently sending the authorized token back to the malicious server.\n\n## TL;DR\nA missing validation of the RFC 9728 'resource' field in the rmcp crate allows rogue MCP servers to perform OAuth resource spoofing and capture legitimate access tokens.\n\n## Exploit Status: POC\n\n## Technical Details\n\n- **CWE ID**: CWE-345\n- **Attack Vector**: Network (AV:N)\n- **CVSS v3.1 Score**: 8.2 (High)\n- **EPSS Score**: N/A\n- **Impact**: Confidentiality High (C:H), Integrity Low (I:L), Scope Changed (S:C)\n- **Exploit Status**: Proof-of-Concept (PoC) available in official test suite\n- **CISA KEV Status**: Not Listed\n\n## Affected Systems\n\n- Model Context Protocol (MCP) clients using the rmcp crate with OAuth features enabled\n- **rmcp**: < 2.0.0 (Fixed in: `2.0.0`)\n\n## Mitigation\n\n- Upgrade the rmcp crate to version 2.0.0 or higher.\n- Disable dynamic OAuth metadata discovery if interacting with untrusted or unverified third-party MCP servers.\n- Enforce egress network controls to restrict outbound metadata discovery requests to trusted hosts only.\n\n**Remediation Steps:**\n1. Open the Cargo.toml of your Rust project containing the rmcp dependency.\n2. Update the dependency entry to: rmcp = { version = \">= 2.0.0\", features = [\"auth\"] }.\n3. Run `cargo update -p rmcp` to update the Cargo.lock file to the patched version.\n4. Verify the updated configuration by rebuilding your client and executing automated verification tests.\n\n## References\n\n- [GHSA-33f5-2c5q-wgwj: OAuth Resource Spoofing Vulnerability in rmcp Crate](https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-33f5-2c5q-wgwj)\n- [Pull Request #937](https://github.com/modelcontextprotocol/rust-sdk/pull/937)\n- [Fix Commit](https://github.com/modelcontextprotocol/rust-sdk/commit/c1a8b29ff2cc45e7820b900dae42cbb4958089ec)\n- [Release rmcp-v2.0.0](https://github.com/modelcontextprotocol/rust-sdk/releases/tag/rmcp-v2.0.0)\n- [CVE-2026-63127 NVD Record](https://www.cve.org/CVERecord?id=CVE-2026-63127)\n\n\n---\n*Generated by [CVEReports](https://cvereports.com/reports/CVE-2026-63127) - Automated Vulnerability Intelligence*", "creation_timestamp": "2026-09-17T03:31:23.799530Z"} 2026-09-17T03:31:23.799530+00:00