CVE-2026-63128 Details
Description
RMCP is an official Rust SDK for the Model Context Protocol. Prior to 2.0.0, the rmcp crate's stateful Streamable HTTP server in crates/rmcp/src/transport/streamable_http_server/tower.rs allows an unauthenticated client to send a well-formed JSON-RPC POST that is not an initialization request, or an initialization request with a mismatched protocol header, causing StreamableHttpService::handle_post to call LocalSessionManager.create_session before validating the message. An early validation failure returns without removing the inserted LocalSessionHandle from LocalSessionManager.sessions, permanently retaining session and channel state for the server process lifetime. Repeated requests can grow the shared session table without bound, degrade legitimate-client latency through lock contention, exhaust memory, and terminate the server. This issue is fixed in version 2.0.0.
A denial-of-service vulnerability has been identified in the RMCP Rust SDK's Streamable HTTP server, prior to version 2.0.0. The issue allows an unauthenticated client to exploit the server's session management by sending well-formed JSON-RPC POST requests that either do not initiate a session or contain mismatched protocol headers. This exploitation causes the server to create a session that is never properly closed, leading to a permanent memory leak. The vulnerability arises from the server's failure to validate messages before allocating session resources, allowing the session table to grow indefinitely with repeated requests. This unchecked session growth exhausts memory and can cause the server to terminate.
Users can update to RMCP Rust SDK version 2.0.0 or later, where this vulnerability has been fixed.
Metrics
CVSS 4.0 Severity and Vector Strings:
VolerionCVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
Volerion
Assessed Sep 16, 2026CISA-ADP
Assessed Sep 16, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-9pj6-vhgr-3mwh | CISA-ADP | AdvisoryExploitRemedyTechnical AnalysisVendor |
| https://github.com/modelcontextprotocol/rust-sdk/commit/dfa7fd6f9309deab60bea230b041be9a3fcda846 | [email protected] | Source CodeVendor |
| https://github.com/modelcontextprotocol/rust-sdk/pull/934 | [email protected] | Issue TrackingVendor |
| https://github.com/modelcontextprotocol/rust-sdk/releases/tag/rmcp-v2.0.0 | [email protected] | Release NotesVendor |
| https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-9pj6-vhgr-3mwh | [email protected] | AdvisoryExploitRemedyTechnical AnalysisVendor |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-400 | Uncontrolled Resource Consumption | [email protected] |
| CWE-401 | Missing Release of Memory after Effective Lifetime | [email protected] |
| CWE-772 | Missing Release of Resource after Effective Lifetime | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| ModelContextProtocol RMCP | <= 1.7.0 (semver) |
CPE
Remediation
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Change History
2 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Sep 16, 2026 | CVE Modified | CISA-ADP |
| Sep 16, 2026 | New CVE Received | [email protected] |