GEM · JULY 2026 · EARLY WARNING

MCP Ruby SDK Vulnerability: Memory Exhaustion Risk Reported

EARLY WARNING · UNCONFIRMED. This page describes a developing threat that 0Day surfaced from early signals and has not yet independently confirmed. Details may change. Always verify against the primary sources before acting.

GHSA-7683-3W9X-CH42GHSA-74GP-QHV5-V493Severity: HIGH

An early warning has been issued regarding a potential vulnerability in the MCP Ruby SDK that could lead to memory exhaustion and denial of service. Users of the mcp-ruby-sdk gem are reportedly affected.

What happened

Reportedly, the MCP Ruby SDK's stdio transports read newline-delimited JSON-RPC frames using `IO#gets` with no limit, which may lead to memory exhaustion and a denial of service. This issue appears to affect versions up to and including the main branch at commit `cf44475c`.

The vulnerability is under investigation, and it is recommended that users upgrade to a version with the fix or apply a patch to limit the buffer size in `IO#gets`. For more detailed information, the primary sources should be consulted.

How 0Day mitigates this

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Read how this differs from waiting on a scanner to catch a known advisory, or see the exact, read-only access 0Day needs to do this for an organization.

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