RMCP: Unauthenticated permanent session-table leak in rmcp Streamable HTTP server transport leads to remote denial-of-service

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-63128
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-16 15:17:39 UTC
Updated2026-09-30 17:51:56 UTC
DescriptionRMCP 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.

Risk And Classification

Primary CVSS: v3.1 7.5 HIGH from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS: 0.006300000 probability, percentile 0.483720000 (date 2026-10-05)

Problem Types: CWE-400 | CWE-401 | CWE-772 | CWE-400 CWE-400: Uncontrolled Resource Consumption | CWE-401 CWE-401: Missing Release of Memory after Effective Lifetime | CWE-772 CWE-772: Missing Release of Resource after Effective Lifetime

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.1CNADECLARED7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Modelcontextprotocol Rust-sdk affected < 2.0.0 Not specified

References

ReferenceSourceLinkTags
github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-9pj6-v... 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
github.com/modelcontextprotocol/rust-sdk/releases/tag/rmcp-v2.0.0 [email protected] github.com
github.com/modelcontextprotocol/rust-sdk/pull/934 [email protected] github.com
github.com/modelcontextprotocol/rust-sdk/commit/dfa7fd6f9309deab60bea230... [email protected] github.com
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