MCP Ruby SDK: Insufficient Session Binding Allows SSE Stream Hijacking via Session ID Replay
Summary
| CVE | CVE-2026-33946 |
|---|---|
| State | PUBLISHED |
| Assigner | GitHub_M |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-03-27 22:16:21 UTC |
| Updated | 2026-04-02 15:23:21 UTC |
| 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. |
Risk And Classification
Primary CVSS: v4.0 8.2 HIGH from [email protected]
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS: 0.000420000 probability, percentile 0.126650000 (date 2026-04-07)
Problem Types: CWE-384 | CWE-639 | CWE-384 CWE-384: Session Fixation | CWE-639 CWE-639: Authorization Bypass Through User-Controlled Key
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 4.0 | [email protected] | Secondary | 8.2 | HIGH | 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/E:X/C... |
| 4.0 | CNA | DECLARED | 8.2 | HIGH | 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 |
| 3.1 | [email protected] | Primary | 5.9 | MEDIUM | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N |
CVSS v4.0 Breakdown
Attack Vector
NetworkAttack Complexity
LowAttack Requirements
PresentPrivileges Required
NoneUser Interaction
NoneConfidentiality
HighIntegrity
NoneAvailability
NoneSub Conf.
NoneSub Integrity
NoneSub Availability
NoneCVSS: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/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
HighPrivileges Required
NoneUser Interaction
NoneScope
UnchangedConfidentiality
HighIntegrity
NoneAvailability
NoneCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
NVD Known Affected Configurations (CPE 2.3)
| Type | Vendor | Product | Version | Update | Edition | Language |
|---|---|---|---|---|---|---|
| Application | Lfprojects | Mcp Ruby Sdk | All | All | All | All |
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Modelcontextprotocol | Ruby-sdk | affected < 0.9.2 | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/stre... | [email protected] | github.com | Patch |
| github.com/modelcontextprotocol/ruby-sdk/blob/main/examples/streamable_h... | [email protected] | github.com | Patch |
| github.com/modelcontextprotocol/go-sdk/blob/main/mcp/streamable.go | [email protected] | github.com | Patch |
| github.com/modelcontextprotocol/csharp-sdk/blob/main/src/ModelContextPro... | [email protected] | github.com | Patch |
| github.com/modelcontextprotocol/ruby-sdk/commit/db40143402d65b4fb6923cec... | [email protected] | github.com | Patch |
| github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.9.2 | [email protected] | github.com | Product, Release Notes |
| github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-qvqr-5... | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | github.com | Exploit, Vendor Advisory |
| hackerone.com/reports/3556146 | [email protected] | hackerone.com | Permissions Required |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
No vendor comments have been submitted for this CVE.
There are currently no legacy QID mappings associated with this CVE.