CVE-2026-33946
Prior to version 0.9.2, the Ruby SDK's streamable_http_transport.rb implementation contains a session hijacking vulnerability.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.46%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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.
- CVSS 4.0
- 8.2 HIGHCVSS:4.0/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/M
- EPSS
- 0.46% probability · 39th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-384, CWE-639
- Affected
- lfprojects/mcp ruby sdk
- Source
- security-advisories@github.com
References
- https://github.com/modelcontextprotocol/csharp-sdk/blob/main/src/ModelContextProtocol.AspNetCore/SseHandler.cs#L93-L97Patch
- https://github.com/modelcontextprotocol/go-sdk/blob/main/mcp/streamable.go#L281C1-L288C2Patch
- https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/streamable_http.py#L680-L685Patch
- https://github.com/modelcontextprotocol/ruby-sdk/blob/main/examples/streamable_http_server.rbPatch
- https://github.com/modelcontextprotocol/ruby-sdk/commit/db40143402d65b4fb6923cec42d2d72cb89b3874Patch
- https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.9.2Product, Release Notes
- https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-qvqr-5cv7-wh35Exploit, Vendor Advisory
- https://hackerone.com/reports/3556146Permissions Required
- https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-qvqr-5cv7-wh35Exploit, Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.