MCP Ruby SDK is the official Ruby SDK for Model Context Protocol servers and clients. Prior to 0.23.0, MCP::Server::Transports::StreamableHTTPTransport in the mcp gem does not bind a session ID to a session owner, allowing an attacker with a stolen session ID to send tools/call requests that execute in the victim's session. This issue is fixed in version 0.23.0.
CVE-2026-67431
HIGHPre-NVD 8.38.3—Trending — 3 sources updated this weekElevated
EchelonGraph scoreMEDIUM confidence
This high-severity CVE scores 8.3 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.3%, top 80% 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, secondary
8.3EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
- High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 8.3Exploit: Elevated riskExposed: 0
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 8.3
- EG Score
- 8.3(medium)
- EG Risk
- 68(Attend)EG Risk 68/100SSVC: 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 computedSeverity83% × 45%Exploitation40% × 40%Automatability100% × 15%Action: Remediate soon — notable exploitation risk. - EPSS PROB
- 0%
- EPSS %ILE
- 20%
- KEV
- Not listed
Published
July 29, 2026
Last Modified
July 30, 2026
Advisory Details (3)
Auto-updated Jul 29, 2026🔬 Proof of concept available. Patch available. Sources: github_release, github, github_commit.
github_release Patch Available
v0.23.0
Patch available: modelcontextprotocol/ruby-sdk v0.23.0
https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0github_commit Patch Available
commit 35466605319a (modelcontextprotocol/ruby-sdk)
Patch available: modelcontextprotocol/ruby-sdk v0.23.0 (contains commit 35466605319a)
https://github.com/modelcontextprotocol/ruby-sdk/commit/35466605319a34e4c7808712ae9bb1ca1afb2356github Patch Available🟡 PoC Available
Ruby SSE Session Poisoning · Advisory · modelcontextprotocol/ruby-sdk · GitHub
https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-5p9g-j988-pcwvVendor Advisories for CVE-2026-67431(1)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
Affected Packages
(1 across 1 ecosystem)
RubyGems(1)
| Package | Vulnerable range | Fixed in | Dependents |
|---|---|---|---|
| mcp | 0.1.0 ... 0.9.2 (25 versions) | 0.23.0 | — |
Weakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 7× in last 7d / 7× 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.
- 2026-07-30 19:42 UTCEG score recompute
- 2026-07-30 16:28 UTCEPSS rescore
- 2026-07-30 15:38 UTCEG score recompute
- 2026-07-30 15:00 UTCEG score recompute
- 2026-07-29 20:19 UTCEG score recompute
- 2026-07-29 19:22 UTCEG score recompute
- 2026-07-29 19:22 UTCMITRE cvelistV5first tracked
Related CVEs(same CWE)
Same CWE
10 shownCWE-284
Frequently asked(5)
What is CVE-2026-67431?
CVE-2026-67431 is a high vulnerability published on July 29, 2026. MCP Ruby SDK is the official Ruby SDK for Model Context Protocol servers and clients. Prior to 0.23.0, MCP::Server::Transports::StreamableHTTPTransport in the mcp gem does not bind a session ID to a session owner, allowing an attacker with a stolen session ID to send tools/call requests that…
When was CVE-2026-67431 disclosed?
CVE-2026-67431 was first published in the National Vulnerability Database on July 29, 2026, with the most recent update on July 30, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-67431 actively exploited?
CVE-2026-67431 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 80.1% of all scored CVEs.
What is the CVSS score of CVE-2026-67431?
CVE-2026-67431 has a CVSS v3 base score of 8.3 (NVD).
How do I remediate CVE-2026-67431?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-67431, 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
See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-67431
Is Your Infrastructure Affected by CVE-2026-67431?
EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.