modelcontextprotocol rust-sdk up to 1.x Streamable HTTP Server tower.rs handle_post initialization

Summaryinfo

A vulnerability was found in modelcontextprotocol rust-sdk up to 1.x. It has been rated as problematic. Impacted is the function StreamableHttpService::handle_post of the file crates/rmcp/src/transport/streamable_http_server/tower.rs of the component Streamable HTTP Server. Performing a manipulation results in initialization. This vulnerability was named CVE-2026-63128. The attack may be initiated remotely. There is no available exploit. Upgrading the affected component is advised.

Detailsinfo

A vulnerability, which was classified as problematic, was found in modelcontextprotocol rust-sdk up to 1.x. This affects the function StreamableHttpService::handle_post of the file crates/rmcp/src/transport/streamable_http_server/tower.rs of the component Streamable HTTP Server. The manipulation with an unknown input leads to a initialization vulnerability. CWE is classifying the issue as CWE-665. The product does not initialize or incorrectly initializes a resource, which might leave the resource in an unexpected state when it is accessed or used. This is going to have an impact on availability. The summary by CVE is:

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.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-63128 since 07/15/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Technical details are known, but no exploit is available.

Upgrading to version 2.0.0 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-80823). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Vendor

• modelcontextprotocol

Name

• rust-sdk

Version

• 1.x

Website

• Product: https://github.com/modelcontextprotocol/rust-sdk/

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CPE 2.2info

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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