CVE-2026-33946
MCP Ruby SDK: Insufficient Session Binding Allows SSE Stream Hijacking via Session ID Replay
Description
MCP Ruby SDK is the official Ruby SDK for Model Context Protocol servers and clients. Prior to version 0.9.2, the Ruby SDK's streamable_http_transport.rb implementation contains a session hijacking vulnerability. An attacker who obtains a valid session ID can completely hijack the victim's Server-Sent Events (SSE) stream and intercept all real-time data. Version 0.9.2 contains a patch.
INFO
Published Date :
March 27, 2026, 10:16 p.m.
Last Modified :
April 2, 2026, 3:23 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | MEDIUM | [email protected] | ||||
| CVSS 4.0 | HIGH | [email protected] |
Solution
- Update MCP Ruby SDK to version 0.9.2 or later.
- Apply the patch provided in version 0.9.2.
- Monitor for unauthorized stream access.
Public PoC/Exploit Available at Github
CVE-2026-33946 has a 1 public
PoC/Exploit available at Github.
Go to the Public Exploits tab to see the list.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-33946.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-33946 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-33946
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
RubySec advisory archive CLI plugin for OpenCLI
cli cve opencli rubysec security
JavaScript TypeScript
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-33946 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-33946 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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Initial Analysis by [email protected]
Apr. 02, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N Added CWE CWE-384 Added CPE Configuration OR *cpe:2.3:a:lfprojects:mcp_ruby_sdk:*:*:*:*:*:*:*:* versions up to (excluding) 0.9.2 Added Reference Type GitHub, Inc.: https://github.com/modelcontextprotocol/csharp-sdk/blob/main/src/ModelContextProtocol.AspNetCore/SseHandler.cs#L93-L97 Types: Patch Added Reference Type GitHub, Inc.: https://github.com/modelcontextprotocol/go-sdk/blob/main/mcp/streamable.go#L281C1-L288C2 Types: Patch Added Reference Type GitHub, Inc.: https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/streamable_http.py#L680-L685 Types: Patch Added Reference Type GitHub, Inc.: https://github.com/modelcontextprotocol/ruby-sdk/blob/main/examples/streamable_http_server.rb Types: Patch Added Reference Type GitHub, Inc.: https://github.com/modelcontextprotocol/ruby-sdk/commit/db40143402d65b4fb6923cec42d2d72cb89b3874 Types: Patch Added Reference Type GitHub, Inc.: https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.9.2 Types: Product, Release Notes Added Reference Type GitHub, Inc.: https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-qvqr-5cv7-wh35 Types: Exploit, Vendor Advisory Added Reference Type CISA-ADP: https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-qvqr-5cv7-wh35 Types: Exploit, Vendor Advisory Added Reference Type GitHub, Inc.: https://hackerone.com/reports/3556146 Types: Permissions Required -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Mar. 30, 2026
Action Type Old Value New Value Added Reference https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-qvqr-5cv7-wh35 -
New CVE Received by [email protected]
Mar. 27, 2026
Action Type Old Value New Value Added Description MCP Ruby SDK is the official Ruby SDK for Model Context Protocol servers and clients. Prior to version 0.9.2, the Ruby SDK's streamable_http_transport.rb implementation contains a session hijacking vulnerability. An attacker who obtains a valid session ID can completely hijack the victim's Server-Sent Events (SSE) stream and intercept all real-time data. Version 0.9.2 contains a patch. Added CVSS V4.0 AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Added CWE CWE-384 Added CWE CWE-639 Added Reference https://github.com/modelcontextprotocol/csharp-sdk/blob/main/src/ModelContextProtocol.AspNetCore/SseHandler.cs#L93-L97 Added Reference https://github.com/modelcontextprotocol/go-sdk/blob/main/mcp/streamable.go#L281C1-L288C2 Added Reference https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/streamable_http.py#L680-L685 Added Reference https://github.com/modelcontextprotocol/ruby-sdk/blob/main/examples/streamable_http_server.rb Added Reference https://github.com/modelcontextprotocol/ruby-sdk/commit/db40143402d65b4fb6923cec42d2d72cb89b3874 Added Reference https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.9.2 Added Reference https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-qvqr-5cv7-wh35 Added Reference https://hackerone.com/reports/3556146