What is CVE-2026-63119?

CVE-2026-63119 is a medium-severity vulnerability in Modelcontextprotocol Ruby-Sdk, classified under Uncontrolled Resource Consumption. CVSS score: 6.2/10. Published 2026-07-29.

How severe is CVE-2026-63119?

Medium severity. CVSS v3 base score is 6.2 out of 10.

Resource exhaustion in Modelcontextprotocol Ruby-Sdk

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.

Vulnerability class: DoS (Denial of Service)

EPSS: 0.001 (2.7th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 6.2 (Medium). Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

Affected products

Modelcontextprotocol Ruby-sdk — versions < 0.23.0

Weakness classification (CWE)

References

security-advisories@github.com (x_refsource_CONFIRM)
security-advisories@github.com (x_refsource_MISC)
security-advisories@github.com (x_refsource_MISC)

Frequently asked questions

What is CVE-2026-63119?: CVE-2026-63119 is a medium-severity vulnerability in Modelcontextprotocol Ruby-Sdk, classified under Uncontrolled Resource Consumption. CVSS score: 6.2/10. Published 2026-07-29.
How severe is CVE-2026-63119?: Medium severity. CVSS v3 base score is 6.2 out of 10.