CVE-2026-63119Public exploit

Host process crash via unbounded stdio frame

Published Jul 29, 2026 · Updated Jul 29, 2026

Resource exhaustion in Model Context Protocol Ruby SDK before 0.23.0 allows local users to crash the host process via an unterminated stdio frame. MCP::Server::Transports::StdioTransport and MCP::Client::Stdio call IO#gets without a byte limit, so a newline-free peer stream grows one Ruby String until memory is exhausted. Reachability requires control of the paired stdio stream; typical unsandboxed peers already share host-level execution, while sandboxed-server and HTTP-to-stdio bridge designs create the material boundary.

CVSS severity6.2
Medium
EPSS probability0.13%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in Model Context Protocol Ruby SDK before 0.23.0 allows local users to crash the host process via an unterminated stdio frame. MCP::Server::Transports::StdioTransport and MCP::Client::Stdio call IO#gets without a byte limit, so a newline-free peer stream grows one Ruby String until memory is exhausted. Reachability requires control of the paired stdio stream; typical unsandboxed peers already share host-level execution, while sandboxed-server and HTTP-to-stdio bridge designs create the material boundary.

The record

CVE
CVE-2026-63119
Published
Jul 29, 2026
Updated
Jul 29, 2026
Vendor
Model Context Protocol
Product
Ruby SDK
Classifications
CWE-770, CWE-400, T1499
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 29, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 29, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 0.23.0

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Model Context Protocol · Ruby SDKversion=< 0.23.0

Published CVSS scores

6.2GitHubCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
CWE-400Uncontrolled Resource Consumption
T1499Endpoint Denial of Service

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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