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

🗓️ 27 Mar 2026 18:36:45Reported by GitHub Advisory DatabaseType 
github
 github🔗 github.com👁 8 Views

Ruby SSE hijack via session identifier replay; lacks binding, ownership checks, and overwrites existing stream.

Related
Detection
Refs
ReporterTitlePublishedViews
Family
ATTACKERKB		CVE-2026-33946
27 Mar 202621:20
–attackerkb
Circl		CVE-2026-33946
27 Mar 202603:31
–circl
CNNVD		MCP Ruby SDK 安全漏洞
27 Mar 202600:00
–cnnvd
CVE		CVE-2026-33946
27 Mar 202621:20
–cve
Cvelist		CVE-2026-33946 MCP Ruby SDK: Insufficient Session Binding Allows SSE Stream Hijacking via Session ID Replay
27 Mar 202621:20
–cvelist
EUVD		EUVD-2026-16866
27 Mar 202621:20
–euvd
NVD		CVE-2026-33946
27 Mar 202622:16
–nvd
OSV		CVE-2026-33946 MCP Ruby SDK: Insufficient Session Binding Allows SSE Stream Hijacking via Session ID Replay
27 Mar 202621:20
–osv
OSV		GHSA-QVQR-5CV7-WH35 MCP Ruby SDK: Insufficient Session Binding Allows SSE Stream Hijacking via Session ID Replay
27 Mar 202618:36
–osv
Positive Technologies		PT-2026-28576
27 Mar 202600:00
–ptsecurity
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Vulners
Node
mcpRange≤0.9.1rubygems
SourceLink
githubwww.github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-qvqr-5cv7-wh35
githubwww.github.com/modelcontextprotocol/ruby-sdk/commit/db40143402d65b4fb6923cec42d2d72cb89b3874
hackeronewww.hackerone.com/reports/3556146
githubwww.github.com/modelcontextprotocol/csharp-sdk/blob/main/src/ModelContextProtocol.AspNetCore/SseHandler.cs
githubwww.github.com/modelcontextprotocol/go-sdk/blob/main/mcp/streamable.go
githubwww.github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/streamable_http.py
githubwww.github.com/modelcontextprotocol/ruby-sdk/blob/main/examples/streamable_http_server.rb
githubwww.github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.9.2
nvdwww.nvd.nist.gov/vuln/detail/CVE-2026-33946
githubwww.github.com/rubysec/ruby-advisory-db/blob/master/gems/mcp/CVE-2026-33946.yml
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30 Mar 2026 20:10Current
5.9Medium risk
Vulners AI Score5.9
CVSS 3.15.9
CVSS 48.2
EPSS0.00064
SSVC
CWE-384CWE-639
session hijackingserver sent eventssession identifierstream overrideownership validationmultiple connectionsbinding to user
8