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.
Published: 2026-09-16
Score: 7.5 High
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
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Remediation

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History

Wed, 16 Sep 2026 16:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Wed, 16 Sep 2026 15:00:00 +0000

Type Values Removed Values Added
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.
Title RMCP: Unauthenticated permanent session-table leak in rmcp Streamable HTTP server transport leads to remote denial-of-service
Weaknesses CWE-400
CWE-401
CWE-772
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}

Subscriptions

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cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-09-16T15:18:37.976Z

Reserved: 2026-07-15T16:54:55.816Z

Link: CVE-2026-63128

cve-icon Vulnrichment

Updated: 2026-09-16T15:18:25.854Z

cve-icon NVD

Status : Received

Published: 2026-09-16T15:17:39.960

Modified: 2026-09-16T16:17:14.440

Link: CVE-2026-63128

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

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Weaknesses
  • CWE-400

    Uncontrolled Resource Consumption

  • CWE-401

    Missing Release of Memory after Effective Lifetime

  • CWE-772

    Missing Release of Resource after Effective Lifetime