CVE-2026-63119: DoS (CVSS 6.2)

Description

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.

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CVSS v3.1 Score

6.2

MEDIUM

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

EPSS — Exploit Prediction

0.0013

Probability of exploitation

0.03%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-400 Uncontrolled Resource Consumption

CWE-770 CWE-770

References

Other References

https://github.com/modelcontextprotocol/ruby-sdk/commit/267b8fa6285453525c81ce43db6b7dcd7a8a8c2f https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0 https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-7683-3w9x-ch42 https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-7683-3w9x-ch42

Frequently Asked Questions

What is CVE-2026-63119? +

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. It has a CVSS v3.1 base score of 6.2 (MEDIUM).

How severe is CVE-2026-63119? +

CVE-2026-63119 has a CVSS v3.1 score of 6.2 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0013, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-63119? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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