high8.2
CVE-2026-33946
MCP Ruby SDK: Insufficient Session Binding Allows SSE Stream Hijacking via Session ID Replay
Impact
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.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| rubygems | mcp | <= 0.9.1 | 0.9.2 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Lfprojects | Mcp Ruby Sdk | before 0.9.2 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/modelcontextprotocol/csharp-sdk/blob/main/src/ModelContextProtocol.AspNetCore/SseHandler.cs#L93-L97
- https://github.com/modelcontextprotocol/go-sdk/blob/main/mcp/streamable.go#L281C1-L288C2
- https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/streamable_http.py#L680-L685
- https://github.com/modelcontextprotocol/ruby-sdk/blob/main/examples/streamable_http_server.rb
- https://github.com/modelcontextprotocol/ruby-sdk/commit/db40143402d65b4fb6923cec42d2d72cb89b3874
- https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.9.2
- https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-qvqr-5cv7-wh35
- https://hackerone.com/reports/3556146
- https://github.com/advisories/GHSA-qvqr-5cv7-wh35
- https://nvd.nist.gov/vuln/detail/CVE-2026-33946
- https://github.com/rubysec/ruby-advisory-db/blob/master/gems/mcp/CVE-2026-33946.yml