High 8.2Published Mar 27, 2026

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

Updated under an hour ago (Oct 26, 2026, 11:10 PM ET)

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It affects modelcontextprotocol ruby-sdk and 1 other product. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

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Every CVE for modelcontextprotocol ruby-sdk

Exploited in the last 30 days

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: 8.2 HIGH (v4.0, CNA)CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
Weakness (CWE): CWE-384, CWE-639
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Analyzed
Record last updated: Mar 30, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

modelcontextprotocol ruby-sdk modelcontextprotocol:ruby_sdk (from the name)	before 0.9.2	CNA record
lfprojects mcp_ruby_sdk lfprojects:mcp_ruby_sdk	before 0.9.2	NVD

References

References

https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-qvqr-5cv7-wh35	x-refsource-confirm, exploit, vendor-advisory
https://github.com/modelcontextprotocol/ruby-sdk/commit/db40143402d65b4fb6923cec42d2d72cb89b3874	x-refsource-misc, patch
https://hackerone.com/reports/3556146	x-refsource-misc, permissions-required
https://github.com/modelcontextprotocol/csharp-sdk/blob/main/src/ModelContextProtocol.AspNetCore/SseHandler.cs#L93-L97	x-refsource-misc, patch
https://github.com/modelcontextprotocol/go-sdk/blob/main/mcp/streamable.go#L281C1-L288C2	x-refsource-misc, patch
https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/streamable_http.py#L680-L685	x-refsource-misc, patch
https://github.com/modelcontextprotocol/ruby-sdk/blob/main/examples/streamable_http_server.rb	x-refsource-misc, patch
https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.9.2	x-refsource-misc, product, release-notes

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.