CVE-2026-67430

MEDIUMPre-NVD 5.35.3—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 5.3 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.3%, top 77% 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
5.3EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.3Exploit: 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 expire sessions by default, so repeated initialize requests retain unbounded ServerSession objects and can exhaust process memory. This issue is fixed in version 0.23.0.

CVSS v3
5.3
EG Score
5.3(medium)
EG Risk
55(Attend)
EG Risk 55/100SSVC: 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
Severity53% × 45%
Exploitation40% × 40%
Automatability100% × 15%
Action: Remediate soon — notable exploitation risk.
EPSS PROB
0%
EPSS %ILE
23%
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, github_commit, github_release.
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 afb968c468c1 (modelcontextprotocol/ruby-sdk)

Patch available: modelcontextprotocol/ruby-sdk v0.23.0 (contains commit afb968c468c1)

https://github.com/modelcontextprotocol/ruby-sdk/commit/afb968c468c178c4d3294b423fcce250621692f4
github Patch Available🟡 PoC Available

Unbounded session retention in StreamableHTTPTransport allows memory exhaustion via initialize flood · Advisory · modelcontextprotocol/ruby-sdk · GitHub

https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-52jp-gj8w-j6xh

Vendor Advisories for CVE-2026-67430(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 10× 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. 2026-08-30 01:22 UTCEPSS rescore
  2. 2026-08-29 23:08 UTCEG score recompute
  3. 2026-08-28 21:42 UTCEPSS rescore
  4. 2026-08-27 20:55 UTCEG score recompute
  5. 2026-08-26 22:12 UTCEG score recompute
  6. 2026-08-26 14:47 UTCEPSS rescore
  7. 2026-08-26 00:35 UTCEG score recompute
  8. 2026-08-25 13:49 UTCEPSS rescore
  9. 2026-08-25 02:35 UTCEG score recompute
  10. 2026-08-23 07:19 UTCEG score recompute
  11. 2026-08-23 00:19 UTCEPSS rescore
  12. 2026-08-22 09:41 UTCEG score recompute
  13. 2026-08-21 23:49 UTCEPSS rescore
  14. 2026-08-21 12:03 UTCEG score recompute
  15. 2026-08-20 22:56 UTCEPSS rescore
  16. 2026-08-20 14:25 UTCEG score recompute
  17. 2026-08-19 17:04 UTCEPSS rescore
  18. 2026-08-18 18:39 UTCEG score recompute
  19. 2026-08-18 13:48 UTCEPSS rescore
  20. 2026-08-17 21:00 UTCEG score recompute
  21. 2026-08-17 13:47 UTCEPSS rescore
  22. 2026-08-16 23:22 UTCEG score recompute
  23. 2026-08-16 14:56 UTCEPSS rescore
  24. 2026-08-15 04:06 UTCEG score recompute
  25. 2026-08-15 01:30 UTCEPSS rescore
Show 32 more
  1. 2026-08-14 06:28 UTCEG score recompute
  2. 2026-08-13 22:00 UTCEPSS rescore
  3. 2026-08-13 08:50 UTCEG score recompute
  4. 2026-08-12 13:51 UTCEPSS rescore
  5. 2026-08-12 11:13 UTCEG score recompute
  6. 2026-08-11 13:35 UTCEG score recompute
  7. 2026-08-11 00:00 UTCEPSS rescore
  8. 2026-08-09 17:52 UTCEG score recompute
  9. 2026-08-09 13:47 UTCEPSS rescore
  10. 2026-08-08 20:15 UTCEG score recompute
  11. 2026-08-08 16:37 UTCEPSS rescore
  12. 2026-08-07 22:37 UTCEG score recompute
  13. 2026-08-07 00:59 UTCEG score recompute
  14. 2026-08-06 13:47 UTCEPSS rescore
  15. 2026-08-06 03:22 UTCEG score recompute
  16. 2026-08-05 19:17 UTCEPSS rescore
  17. 2026-08-05 19:17 UTCEPSS rescore
  18. 2026-08-05 05:44 UTCEG score recompute
  19. 2026-08-04 15:10 UTCEPSS rescore
  20. 2026-08-04 10:39 UTCEPSS rescore
  21. 2026-08-04 08:06 UTCEG score recompute
  22. 2026-08-03 10:36 UTCEPSS rescore
  23. 2026-08-02 12:37 UTCEG score recompute
  24. 2026-08-02 02:27 UTCEPSS rescore
  25. 2026-08-01 14:59 UTCEG score recompute
  26. 2026-08-01 04:16 UTCEPSS rescore
  27. 2026-07-30 16:34 UTCEG score recompute
  28. 2026-07-30 16:28 UTCEPSS rescore
  29. 2026-07-30 15:40 UTCEG score recompute
  30. 2026-07-29 20:20 UTCEG score recompute
  31. 2026-07-29 19:23 UTCEG score recompute
  32. 2026-07-29 19:22 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-67430?
CVE-2026-67430 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 expire sessions by default, so repeated initialize requests retain unbounded ServerSession objects and can exhaust process…
When was CVE-2026-67430 disclosed?
CVE-2026-67430 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-2026-67430 actively exploited?
CVE-2026-67430 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 76.9% of all scored CVEs.
What is the CVSS score of CVE-2026-67430?
CVE-2026-67430 has a CVSS v3 base score of 5.3 (NVD).
How do I remediate CVE-2026-67430?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-67430, 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-2026-67430

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