CVE-2026-63118

MEDIUMPre-NVD 6.96.9—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 6.9 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.3% (15th percentile of EPSS-scored CVEs). 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
Elevated
6.9EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0.3%CVSS: 6.9Exploit: Elevated riskExposed services: Not assessed

A fix is available — apply it.

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 validate the HTTP Host or Origin request headers, which allows a malicious browser page to use DNS rebinding to reach a locally running MCP server and invoke exposed tools. This issue is fixed in version 0.23.0.

CVSS v3
6.9
EG Score
6.9MEDIUMmedium confidence
EG Risk
47
EG Risk 47/100CISA SSVC

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
Severity69% × 45%
Exploitation40% × 40%
Automatability0% × 15%
CISA SSVC: Track at low or medium mission impact; Track* at high (mission-essential systems).
Action: A fix is available. Apply it within your standard update timelines.
EPSS PROB
0.3%
EPSS %ILE
15th
KEV
Not listed

CISA SSVCTrack at low or medium mission impact; Track* at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines.

Exploitation public PoC (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table

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_commit, github_release, github.
github_release Patch Available

v0.23.0

Patch available: modelcontextprotocol/ruby-sdk v0.23.0

https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0
github_commit Patch Available

commit ba543083a759 (modelcontextprotocol/ruby-sdk)

Patch available: modelcontextprotocol/ruby-sdk v0.23.0 (contains commit ba543083a759)

https://github.com/modelcontextprotocol/ruby-sdk/commit/ba543083a7594e7892b29464b89091816446ff7a
githubMentions a patch (unverified)🟡 PoC Available

Streamable HTTP transport lacks DNS-rebinding (Host/Origin) protection · Advisory · modelcontextprotocol/ruby-sdk · GitHub

https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-rjr6-rcgv-9m7m

Vendor Advisories for CVE-2026-63118(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)
PackageVulnerable rangeFix by version rangeDependents
mcp0.1.0 ... 0.9.2 (25 versions)
  • every version up to 0.23.0: fixed in 0.23.0
—

Weakness Classification(2)

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

Data Freshness Timeline

(refreshed 10× in last 7d / 39× 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 113 total refreshes for this CVE.

  1. 2026-10-09 20:07 UTCEPSS rescore
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  3. 2026-10-07 23:48 UTCEPSS rescore
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  1. 2026-09-19 04:49 UTCEG score recompute
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Frequently asked(5)

What is CVE-2026-63118?
CVE-2026-63118 is a medium 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 validate the HTTP Host or Origin request headers, which allows a malicious browser page to use DNS rebinding to reach a…
When was CVE-2026-63118 disclosed?
CVE-2026-63118 was first published 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-2026-63118 actively exploited?
CVE-2026-63118 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.3% probability of exploitation in the next 30 days (15th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-63118?
CVE-2026-63118 has a CVSS base score of 6.9 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-63118?
A fix for CVE-2026-63118 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-63118 are linked in the Vendor Advisories panel on this page.

Dependency Blast Radius

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