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CVE-2026-63128— RMCP: Unauthenticated permanent session-table leak in rmcp Streamable HTTP server transport leads to remote denial-of-service

Quick assessment

Affected
modelcontextprotocol rust-sdk
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

RMCP 是模型上下文协议（Model Context Protocol, MCP）的官方 Rust SDK。在 2.0.0 版本之前， crate 中基于有状态 Streamable HTTP 服务器的实现（位于 ）允许未认证客户端发送格式正确但并非初始化请求的 JSON-RPC POST，或携带不匹配协议头的初始化请求，导致 在验证消息之前就先调用了 。若早期验证失败，函数会在移除已插入的 之前直接返回，从而导致该会话及其通道状态在服务器进程整个生命周期内被永久保留。反复发送此类请求会导致共享会话表无限增长，因

CVSS 7.5 · High
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I. Basic Information for CVE-2026-63128

Vulnerability Information
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Vulnerability Title
RMCP: Unauthenticated permanent session-table leak in rmcp Streamable HTTP server transport leads to remote denial-of-service
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
未加控制的资源消耗(资源穷尽)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
modelcontextprotocol rust-sdk < 2.0.0 -

II. Public POCs for CVE-2026-63128

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III. Intelligence Information for CVE-2026-63128

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Patches & Fixes for CVE-2026-63128 (2)

Vendor Advisories for CVE-2026-63128 (1)

Vendor Pages for CVE-2026-63128 (1)

IV. Related Vulnerabilities

Same product: rust-sdk
Same vendor: modelcontextprotocol
Same weakness: CWE-400

V. Comments for CVE-2026-63128

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