Vulnerability in Rust SDK's Streamable HTTP Server Affects Model Context Protocol Products
CVE-2026-63128

7.5HIGH

Key Information:

Vendor

Modelcontextprotocol

Status
Rust-sdk
Vendor
CVE Published:
16 September 2026

What is CVE-2026-63128?

The Rust SDK for the Model Context Protocol features a flaw within its stateful Streamable HTTP server that permits unauthenticated clients to send well-formed JSON-RPC POST requests. This vulnerability arises from insufficient validation of incoming messages prior to creating sessions. Consequently, the LocalSessionManager retains the session state indefinitely despite validation failures, which can lead to an uncontrollable growth of the shared session table. This could exhaust memory resources and degrade performance by causing contention and latency for legitimate clients. The issue has been rectified in version 2.0.0.

Affected Version(s)

rust-sdk < 2.0.0

References

https://github.com/modelcontextprotocol/rust-sdk/security...
x_refsource_CONFIRM
https://github.com/modelcontextprotocol/rust-sdk/pull/934
x_refsource_MISC
https://github.com/modelcontextprotocol/rust-sdk/commit/d...
x_refsource_MISC

CVSS V3.1

Score:
7.5
Severity:
HIGH
Confidentiality:
None
Integrity:
None
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.