CVE-2026-33946

RubyGems/mcp CVE-2026-33946: high, EPSS 0.54%

MCP Ruby SDK: Insufficient Session Binding Allows SSE Stream Hijacking via Session ID Replay

Action: Upgrade mcp to 0.9.2 or later.

bundle update mcp

Affected

Fixed versions

Sources

• osv: GHSA-qvqr-5cv7-wh35
• https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-qvqr-5cv7-wh35
• https://nvd.nist.gov/vuln/detail/CVE-2026-33946
• https://github.com/modelcontextprotocol/ruby-sdk/commit/db40143402d65b4fb6923cec42d2d72cb89b3874
• https://hackerone.com/reports/3556146
• 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
• https://github.com/modelcontextprotocol/ruby-sdk/blob/main/examples/streamable_http_server.rb
• https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.9.2
• https://github.com/rubysec/ruby-advisory-db/blob/master/gems/mcp/CVE-2026-33946.yml

CVE-2026-33946 · published 2026-03-27T18:36:45Z · modified 2026-03-30T20:19:48.069207Z · JSON