# CVE-2026-33946: MCP Ruby SDK: Insufficient Session Binding Allows SSE Stream Hijacking via Session ID Replay

Source: https://junglewise.ai/threats/cve-2026-33946-mcp-ruby-sdk-insufficient-session-binding-allows-sse-stream  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-03-27  
License: CC BY 4.0 with a link back

CVE-2026-33946 · Severity: medium · CVSS 5.9 · Published 2026-03-27

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.

Technologies: [mcp (RubyGems)](https://junglewise.ai/threats/technologies/rubygems-mcp). Vendors: [Lfprojects](https://junglewise.ai/threats/vendors/lfprojects), [RubyGems](https://junglewise.ai/threats/vendors/rubygems).

## Quick answers

**Is CVE-2026-33946 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-33946 being exploited in the wild.

**How severe is CVE-2026-33946?** Medium severity, with a CVSS score of 5.9, published 27 March 2026.

**Which products and versions are affected?** mcp (RubyGems) ECOSYSTEM:introduced=0,fixed=0.9.2.

**Is there a fix for CVE-2026-33946?** Yes. mcp (RubyGems): upgrade to 0.9.2 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2026-33946?** Check whether you run Lfprojects Mcp Ruby Sdk or mcp (RubyGems) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- mcp (RubyGems): upgrade to 0.9.2 or later

  ```sh
  bundle update mcp
  ```


## Affected products

- Lfprojects Mcp Ruby Sdk
- mcp (RubyGems) ECOSYSTEM:introduced=0,fixed=0.9.2

## Identifiers

- CVE-2026-33946
- GHSA-qvqr-5cv7-wh35

## Related threats

- [Model Context Protocol Ruby SDK memory exhaustion in StreamableHTTPTransport](https://junglewise.ai/threats/cve-2026-67432-model-context-protocol-ruby-sdk-memory-exhaustion-in)
- [modelcontextprotocol ruby-sdk session hijacking in StreamableHTTPTransport](https://junglewise.ai/threats/cve-2026-67431-modelcontextprotocol-ruby-sdk-session-hijacking-in)
- [Model Context Protocol Ruby SDK memory exhaustion in StreamableHTTPTransport](https://junglewise.ai/threats/cve-2026-67430-model-context-protocol-ruby-sdk-memory-exhaustion-in)
- [modelcontextprotocol ruby-sdk memory exhaustion in Stdio transports](https://junglewise.ai/threats/cve-2026-63119-modelcontextprotocol-ruby-sdk-memory-exhaustion-in-stdio)
- [modelcontextprotocol ruby-sdk DNS rebinding in StreamableHTTPTransport](https://junglewise.ai/threats/cve-2026-63118-modelcontextprotocol-ruby-sdk-dns-rebinding-in)