CVE-2026-33946

MEDIUMNVD 5.95.9—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 5.9 under NVD CVSS v3. EPSS exploit probability: 0.5%, top 62% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
Elevated
5.9EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.9Exploit: Elevated riskExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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 v3
5.9
EG Score
5.9(medium)
EG Risk
58(Attend)
EG Risk 58/100SSVC: Attend

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity59% × 45%
Exploitation40% × 40%
Automatability100% × 15%
Action: Remediate soon — notable exploitation risk.
EPSS PROB
0%
EPSS %ILE
39%
KEV
Not listed

Published

March 27, 2026

Last Modified

June 17, 2026

Advisory Details (7)

Auto-updated Aug 3, 2026
🔬 Proof of concept available. Patch available. Sources: github_commit, github_release, github.
github Patch Available🟡 PoC Available

Lack of Session Hijacking protection in ruby-sdk - Stream Replacement Vulnerability · Advisory · modelcontextprotocol/ruby-sdk · GitHub

https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-qvqr-5cv7-wh35
github_release Patch Available

v0.9.2

Patch available: modelcontextprotocol/ruby-sdk v0.9.2

https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.9.2
github_commit Patch Available

commit db40143402d6 (modelcontextprotocol/ruby-sdk)

Patch available: modelcontextprotocol/ruby-sdk v0.9.2 (contains commit db40143402d6)

https://github.com/modelcontextprotocol/ruby-sdk/commit/db40143402d65b4fb6923cec42d2d72cb89b3874
generic

ruby-sdk/examples/streamable_http_server.rb at main · modelcontextprotocol/ruby-sdk · GitHub

https://github.com/modelcontextprotocol/ruby-sdk/blob/main/examples/streamable_http_server.rb
generic

python-sdk/src/mcp/server/streamable_http.py at main · modelcontextprotocol/python-sdk · GitHub

https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/streamable_http.py#L680-L685
generic

go-sdk/mcp/streamable.go at main · modelcontextprotocol/go-sdk · GitHub

https://github.com/modelcontextprotocol/go-sdk/blob/main/mcp/streamable.go#L281C1-L288C2
generic

csharp-sdk/src/ModelContextProtocol.AspNetCore/SseHandler.cs at main · modelcontextprotocol/csharp-sdk · GitHub

https://github.com/modelcontextprotocol/csharp-sdk/blob/main/src/ModelContextProtocol.AspNetCore/SseHandler.cs#L93-L97

Affected Packages

(1 across 1 ecosystem)
RubyGems(1)
PackageVulnerable rangeFixed inDependents
mcp0.1.0 ... 0.9.1 (11 versions)0.9.2—

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 6× in last 7d / 28× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 164 total refreshes for this CVE.

  1. 2026-09-15 03:11 UTCEPSS rescore
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Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-33946?
CVE-2026-33946 is a medium vulnerability published on March 27, 2026. 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 streamablehttptransport.rb implementation contains a session hijacking vulnerability. An attacker who obtains a valid session ID can completely hijack the victim's…
When was CVE-2026-33946 disclosed?
CVE-2026-33946 was first published in the National Vulnerability Database on March 27, 2026, with the most recent update on June 17, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-33946 actively exploited?
CVE-2026-33946 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 61.0% of all scored CVEs.
What is the CVSS score of CVE-2026-33946?
CVE-2026-33946 has a CVSS v3 base score of 5.9 (NVD).
How do I remediate CVE-2026-33946?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-33946, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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