CVE-2026-67431

HIGHPre-NVD 8.38.3
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to the CVSS score beside it.

This high-severity CVE scores 8.3 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.4% (30th percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.

Triggered by: Headline CVSS from a secondary CVSS source
Sources: EPSS, a secondary CVSS source
Elevated

Also known asEUVD-2026-50501 (ENISA EUVD) · GHSA-5p9g-j988-pcwv (GitHub Security Advisories)Source: ENISA EUVD

8.3EG
EchelonGraph verdictPlan a fixRemediate within your standard update timelines at low or medium mission impact and sooner than that at high (the SSVC decision on this page).
  • CISA's Vulnrichment rates exploitation as PoC; EchelonGraph holds no exploit-code reference for it
CISA-KEV: Not listedEPSS PROB: 0.4%CVSS: 8.3Exploit: No code on recordExposed 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 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.

CVSS
8.3
EG Score
8.3HIGHmedium confidence
EG Risk
68
EG Risk 68/100

EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.

How it’s computed (value × EchelonGraph’s weight)
Severity83% × 45%
Impact severity (EG Severity): CVSS 8.3 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation40% × 40%
EchelonGraph's fixed weight for EG-KEV Tier 3 (Elevated): a constant, not a probability.
Automatability100% × 15%
CISA's SSVC Automatable value: yes (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at low, Track* at medium and Attend at high mission impact.
Exploitation public PoC (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
EPSS PROB
0.4%
EPSS %ILE
30th
KEV
Not listed

What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)

The EG score (8.3): severity, escalated by confirmed exploitation. This CVE's 8.3 is its impact severity (EG Severity), not escalated.

EG Severity
8.3 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.a secondary CVSS source
EG Likelihood
0.4% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-11-09). FIRST's exploitation probability, not an EchelonGraph model.
Confirmed exploitation
None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
EG Priority
SSVC Track* at medium mission impactTrack at low, Track* at medium and Attend at high mission impact.CISA BOD 26-04: 3 days if the affected system is publicly exposed; 60 days if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.

SSVC (CISA's decision table, applied by EchelonGraph)Track at low, Track* at medium and Attend at high mission impact.

A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.

Exploitation public PoC (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)3 days if the affected system is publicly exposed; 60 days if it is not.

The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable yes (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

July 29, 2026

Last Modified

October 24, 2026

Advisory Details (3)

Auto-updated Jul 29, 2026
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/v0.23.0
GitHub 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/35466605319a34e4c7808712ae9bb1ca1afb2356
GitHub advisoryMentions a patch (unverified)

Ruby SSE Session Poisoning · Advisory · modelcontextprotocol/ruby-sdk · GitHub

https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-5p9g-j988-pcwv

Vendor 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.

Patch Availability(1)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
rubygemsmcp @ 0.23.0 (fixes <= 0.22.0)—ghsa

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

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(1)

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

Data Freshness Timeline

(refreshed 8× in last 7d / 33× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed its CVE.org record (CNA or CISA ADP). An arrow marks a change the record states ("CVSS → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). "EchelonGraph re-scored" is our own recompute of this CVE's score, not an update from a source, and is not counted in the refreshes above. Most recent first.

Showing the most recent 100 of 171 rows on record for this CVE.

A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. None are among the latest 100 rows. The 71 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-11-13 16:53 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  2. 2026-11-12 16:34 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  3. 2026-11-11 16:40 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  4. 2026-11-10 16:45 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  5. 2026-11-09 18:08 UTCEchelonGraph re-scored
  6. 2026-11-09 18:08 UTCGHSA enrichmentGHSA-5p9g-j988-pcwv · GitHub severity HIGH
  7. 2026-11-09 16:36 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  8. 2026-11-08 16:40 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  9. 2026-11-07 16:39 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  10. 2026-11-06 16:39 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  11. 2026-11-05 16:38 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  12. 2026-11-04 16:36 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  13. 2026-11-03 16:48 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  14. 2026-11-03 07:42 UTCEchelonGraph re-scored
  15. 2026-11-03 07:42 UTCGHSA enrichmentGHSA-5p9g-j988-pcwv · GitHub severity HIGH
  16. 2026-11-02 16:45 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  17. 2026-11-01 16:35 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  18. 2026-11-01 07:40 UTCGHSA enrichmentGHSA-5p9g-j988-pcwv · GitHub severity HIGH
  19. 2026-11-01 07:40 UTCEchelonGraph re-scored
  20. 2026-10-31 16:33 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  21. 2026-10-30 16:35 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  22. 2026-10-29 16:33 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  23. 2026-10-28 16:33 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  24. 2026-10-27 21:06 UTCEchelonGraph re-scored
  25. 2026-10-27 16:32 UTCEPSS rescoreEPSS 0.4% · 29th percentile
Show 75 more
  1. 2026-10-26 16:32 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  2. 2026-10-25 16:33 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  3. 2026-10-25 14:10 UTCEchelonGraph re-scored
  4. 2026-10-24 16:33 UTCEPSS rescoreEPSS 0.5% · 40th percentile
  5. 2026-10-24 13:29 UTCEchelonGraph re-scored
  6. 2026-10-23 16:32 UTCEPSS rescoreEPSS 0.5% · 40th percentile
  7. 2026-10-22 16:35 UTCEPSS rescoreEPSS 0.5% · 40th percentile
  8. 2026-10-21 16:33 UTCEPSS rescoreEPSS 0.5% · 40th percentile
  9. 2026-10-20 16:33 UTCEPSS rescoreEPSS 0.5% · 40th percentile
  10. 2026-10-20 09:03 UTCEchelonGraph re-scored
  11. 2026-10-19 16:32 UTCEPSS rescoreEPSS 0.5% · 40th percentile
  12. 2026-10-18 16:32 UTCEPSS rescoreEPSS 0.5% · 40th percentile
  13. 2026-10-18 03:20 UTCEchelonGraph re-scored
  14. 2026-10-17 16:35 UTCEPSS rescoreEPSS 0.5% · 40th percentile
  15. 2026-10-16 16:43 UTCEPSS rescoreEPSS 0.5% · 39th percentile
  16. 2026-10-15 16:32 UTCEPSS rescoreEPSS 0.5% · 39th percentile
  17. 2026-10-14 16:33 UTCEPSS rescoreEPSS 0.5% · 39th percentile
  18. 2026-10-13 16:35 UTCEPSS rescoreEPSS 0.5% · 39th percentile
  19. 2026-10-13 10:23 UTCEchelonGraph re-scored
  20. 2026-10-12 16:34 UTCEPSS rescoreEPSS 0.5% · 39th percentile
  21. 2026-10-12 15:45 UTCEchelonGraph re-scored
  22. 2026-10-11 19:30 UTCEchelonGraph re-scored
  23. 2026-10-11 16:46 UTCEchelonGraph re-scored
  24. 2026-10-11 14:06 UTCEchelonGraph re-scored
  25. 2026-10-11 13:49 UTCEPSS rescoreEPSS 0.5% · 39th percentile
  26. 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.5% · 39th percentile
  27. 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.5% · 39th percentile
  28. 2026-10-08 17:13 UTCEPSS rescoreEPSS 0.5% · 39th percentile
  29. 2026-10-07 23:48 UTCEPSS rescoreEPSS 0.5% · 39th percentile
  30. 2026-10-07 00:00 UTCEchelonGraph re-scored
  31. 2026-10-06 15:18 UTCEPSS rescoreEPSS 0.5% · 39th percentile
  32. 2026-10-05 20:50 UTCEchelonGraph re-scored
  33. 2026-10-05 17:43 UTCEPSS rescoreEPSS 0.5% · 39th percentile
  34. 2026-10-05 00:05 UTCEchelonGraph re-scored
  35. 2026-10-04 23:22 UTCEPSS rescoreEPSS 0.5% · 39th percentile
  36. 2026-10-04 06:58 UTCEchelonGraph re-scored
  37. 2026-10-03 14:26 UTCEPSS rescoreEPSS 0.5% · 39th percentile
  38. 2026-10-02 17:56 UTCEchelonGraph re-scored
  39. 2026-10-02 17:56 UTCEPSS rescoreEPSS 0.5% · 39th percentile
  40. 2026-10-01 19:50 UTCEPSS rescoreEPSS 0.5% · 39th percentile
  41. 2026-10-01 03:32 UTCEchelonGraph re-scored
  42. 2026-09-30 15:03 UTCEPSS rescoreEPSS 0.5% · 39th percentile
  43. 2026-09-29 07:32 UTCEchelonGraph re-scored
  44. 2026-09-28 13:52 UTCEPSS rescoreEPSS 0.5% · 38th percentile
  45. 2026-09-27 19:35 UTCEchelonGraph re-scored
  46. 2026-09-27 13:48 UTCEPSS rescoreEPSS 0.5% · 38th percentile
  47. 2026-09-26 15:59 UTCEPSS rescoreEPSS 0.5% · 38th percentile
  48. 2026-09-25 05:31 UTCEchelonGraph re-scored
  49. 2026-09-23 21:47 UTCEchelonGraph re-scored
  50. 2026-09-23 17:54 UTCEPSS rescoreEPSS 0.3% · 22nd percentile
  51. 2026-09-23 02:52 UTCEchelonGraph re-scored
  52. 2026-09-22 15:45 UTCEchelonGraph re-scored
  53. 2026-09-20 20:16 UTCEPSS rescoreEPSS 0.3% · 22nd percentile
  54. 2026-09-20 00:21 UTCEchelonGraph re-scored
  55. 2026-09-19 04:45 UTCEchelonGraph re-scored
  56. 2026-09-18 19:28 UTCEPSS rescoreEPSS 0.3% · 22nd percentile
  57. 2026-09-18 01:39 UTCEchelonGraph re-scored
  58. 2026-09-17 01:34 UTCEchelonGraph re-scored
  59. 2026-09-16 14:08 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  60. 2026-09-16 05:47 UTCEchelonGraph re-scored
  61. 2026-09-16 05:15 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  62. 2026-09-15 07:47 UTCEchelonGraph re-scored
  63. 2026-09-14 01:43 UTCEchelonGraph re-scored
  64. 2026-09-12 16:20 UTCEchelonGraph re-scored
  65. 2026-09-11 18:03 UTCEchelonGraph re-scored
  66. 2026-09-11 09:37 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  67. 2026-09-10 19:48 UTCEchelonGraph re-scored
  68. 2026-09-09 07:44 UTCEchelonGraph re-scored
  69. 2026-09-08 22:01 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  70. 2026-09-07 20:36 UTCEchelonGraph re-scored
  71. 2026-09-07 16:01 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  72. 2026-09-06 17:56 UTCEchelonGraph re-scored
  73. 2026-09-06 13:47 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  74. 2026-09-05 19:03 UTCEchelonGraph re-scored
  75. 2026-09-05 15:31 UTCEPSS rescoreEPSS 0.3% · 21st percentile

Frequently asked(5)

What is CVE-2026-67431?
CVE-2026-67431 is a high-severity vulnerability; its CVE record was 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 the CVE record for CVE-2026-67431 published?
The CVE record for CVE-2026-67431 was published on July 29, 2026. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of October 24, 2026; the record at its source may have been updated since.
Is CVE-2026-67431 actively exploited?
CVE-2026-67431 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.4% probability of exploitation in the next 30 days (30th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-67431?
CVE-2026-67431 has a CVSS base score of 8.3 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-67431?
A fix for CVE-2026-67431 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-67431 are linked in the Vendor Advisories panel on this page.

Dependency Blast Radius

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