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: 0.2%, top 91% 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
Elevated
6.9EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 6.9Exploit: 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 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
6.9(medium)
EG Risk
47(Track)
EG Risk 47/100SSVC: Track

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%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
9%
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_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
github Patch Available🟡 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 rangeFixed inDependents
mcp0.1.0 ... 0.9.2 (25 versions)0.23.0—

Weakness Classification(2)

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

Data Freshness Timeline

(refreshed 12× in last 7d / 51× 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.

  1. 2026-08-25 22:39 UTCEG score recompute
  2. 2026-08-25 13:49 UTCEPSS rescore
  3. 2026-08-24 23:28 UTCEG score recompute
  4. 2026-08-23 01:04 UTCEG score recompute
  5. 2026-08-23 00:19 UTCEPSS rescore
  6. 2026-08-22 01:52 UTCEG score recompute
  7. 2026-08-21 23:49 UTCEPSS rescore
  8. 2026-08-21 02:40 UTCEG score recompute
  9. 2026-08-20 22:55 UTCEPSS rescore
  10. 2026-08-20 03:28 UTCEG score recompute
  11. 2026-08-19 17:04 UTCEPSS rescore
  12. 2026-08-19 04:13 UTCEG score recompute
  13. 2026-08-18 13:48 UTCEPSS rescore
  14. 2026-08-18 04:59 UTCEG score recompute
  15. 2026-08-17 13:47 UTCEPSS rescore
  16. 2026-08-17 05:47 UTCEG score recompute
  17. 2026-08-16 14:56 UTCEPSS rescore
  18. 2026-08-16 06:10 UTCEG score recompute
  19. 2026-08-15 06:59 UTCEG score recompute
  20. 2026-08-15 01:30 UTCEPSS rescore
  21. 2026-08-14 07:42 UTCEG score recompute
  22. 2026-08-13 22:00 UTCEPSS rescore
  23. 2026-08-13 08:30 UTCEG score recompute
  24. 2026-08-12 13:51 UTCEPSS rescore
  25. 2026-08-12 09:18 UTCEG score recompute
Show 26 more
  1. 2026-08-11 10:06 UTCEG score recompute
  2. 2026-08-11 00:00 UTCEPSS rescore
  3. 2026-08-10 10:54 UTCEG score recompute
  4. 2026-08-09 13:47 UTCEPSS rescore
  5. 2026-08-09 11:42 UTCEG score recompute
  6. 2026-08-08 16:37 UTCEPSS rescore
  7. 2026-08-08 12:28 UTCEG score recompute
  8. 2026-08-06 14:05 UTCEG score recompute
  9. 2026-08-06 13:47 UTCEPSS rescore
  10. 2026-08-05 19:17 UTCEPSS rescore
  11. 2026-08-05 19:17 UTCEPSS rescore
  12. 2026-08-04 15:41 UTCEG score recompute
  13. 2026-08-04 15:10 UTCEPSS rescore
  14. 2026-08-04 10:39 UTCEPSS rescore
  15. 2026-08-03 16:30 UTCEG score recompute
  16. 2026-08-03 10:36 UTCEPSS rescore
  17. 2026-08-02 17:19 UTCEG score recompute
  18. 2026-08-02 02:27 UTCEPSS rescore
  19. 2026-08-01 18:07 UTCEG score recompute
  20. 2026-08-01 04:16 UTCEPSS rescore
  21. 2026-07-30 19:42 UTCEG score recompute
  22. 2026-07-30 16:28 UTCEPSS rescore
  23. 2026-07-29 20:20 UTCEG score recompute
  24. 2026-07-29 19:59 UTCEG score recompute
  25. 2026-07-29 19:23 UTCEG score recompute
  26. 2026-07-29 19:22 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

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 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-2026-63118 actively exploited?
CVE-2026-63118 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 90.8% of all scored CVEs.
What is the CVSS score of CVE-2026-63118?
CVE-2026-63118 has a CVSS v3 base score of 6.9 (NVD).
How do I remediate CVE-2026-63118?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-63118, 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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