MCP Ruby SDK is the official Ruby SDK for Model Context Protocol servers and clients. Prior to 0.23.0, MCP::Server::Transports::StdioTransport and MCP::Client::Stdio in the mcp gem use IO#gets without a byte limit, allowing a peer that sends data without a newline to exhaust process memory. This issue is fixed in version 0.23.0.
CVE-2026-63119
MEDIUMPre-NVD 6.26.2—Trending — 3 sources updated this weekElevated
EchelonGraph scoreMEDIUM confidence
This medium-severity CVE scores 6.2 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.1%, top 97% 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
6.2EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
- Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 6.2Exploit: Elevated riskExposed: 0
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 6.2
- EG Score
- 6.2(medium)
- EG Risk
- 44(Track)EG Risk 44/100SSVC: 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 computedSeverity62% × 45%Exploitation40% × 40%Automatability0% × 15%Action: Routine — remediate on your standard cadence. - EPSS PROB
- 0%
- EPSS %ILE
- 3%
- 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/v0.23.0github_commit Patch Available
commit 267b8fa62854 (modelcontextprotocol/ruby-sdk)
Patch available: modelcontextprotocol/ruby-sdk v0.23.0 (contains commit 267b8fa62854)
https://github.com/modelcontextprotocol/ruby-sdk/commit/267b8fa6285453525c81ce43db6b7dcd7a8a8c2fgithub Patch Available🟡 PoC Available
Unbounded line buffer in stdio transports leads to memory exhaustion (DoS) · Advisory · modelcontextprotocol/ruby-sdk · GitHub
https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-7683-3w9x-ch42Vendor Advisories for CVE-2026-63119(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(2)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 6× in last 7d / 6× 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 19:43 UTCEG score recompute
- 2026-07-30 16:28 UTCEPSS rescore
- 2026-07-29 20:20 UTCEG score recompute
- 2026-07-29 19:59 UTCEG score recompute
- 2026-07-29 19:23 UTCEG score recompute
- 2026-07-29 19:22 UTCMITRE cvelistV5first tracked
Related CVEs(same CWE)
Same CWE
10 shownCWE-400 · CWE-770
- CVE-2004-1464NVD 5.9EG 9.0 KEVEPSS p92CRITICAL
- CVE-2010-3705EG 8.3HIGH
- CVE-2006-1364NVD 7.5EG 8.2EPSS p99HIGH
- CVE-2008-5180NVD 5.3EG 7.9EPSS p99HIGH
- CVE-2012-0024EG 7.8HIGH
- CVE-2011-3192EG 7.8EPSS p100HIGH
- CVE-2010-4686EG 7.8HIGH
- CVE-2010-4671EG 7.8HIGH
- CVE-2009-2054EG 7.8HIGH
- CVE-2009-2726EG 7.8EPSS p93HIGH
Frequently asked(5)
What is CVE-2026-63119?
CVE-2026-63119 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::StdioTransport and MCP::Client::Stdio in the mcp gem use IO#gets without a byte limit, allowing a peer that sends data without a newline to exhaust process memory. This…
When was CVE-2026-63119 disclosed?
CVE-2026-63119 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-2026-63119 actively exploited?
CVE-2026-63119 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 97.0% of all scored CVEs.
What is the CVSS score of CVE-2026-63119?
CVE-2026-63119 has a CVSS v3 base score of 6.2 (NVD).
How do I remediate CVE-2026-63119?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-63119, 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-2026-63119
Is Your Infrastructure Affected by CVE-2026-63119?
EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.