EUVD-2026-50502
GHSA-h669-8m4g-r2hc
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Remote unauthenticated POST with no interaction and low complexity triggers unbounded allocation; impact is availability-only (worker OOM), so C:N/I:N/A:H.
Primary rating from Vendor (GitHub_M).
CVSS VectorVendor: GitHub_M
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Lifecycle Timeline
4DescriptionCVE.org
MCP Ruby SDK is the official Ruby SDK for Model Context Protocol servers and clients. Prior to 0.23.0, MCP::Server::Transports::StreamableHTTPTransport in the mcp gem reads and parses an entire JSON-RPC POST body without a size limit, allowing an unauthenticated remote attacker to exhaust process memory. This issue is fixed in version 0.23.0.
AnalysisAI
Uncontrolled memory allocation in the official Model Context Protocol Ruby SDK (mcp gem) before 0.23.0 lets an unauthenticated remote attacker crash MCP servers by sending a single oversized JSON-RPC POST. The StreamableHTTPTransport read the entire request body into memory and parsed it with no size or JSON-nesting cap, so one request can allocate gigabytes and OOM-kill the worker (CVSS 7.5, availability-only impact). …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | The MCP server must expose MCP::Server::Transports::StreamableHTTPTransport over HTTP to the attacker (the Streamable HTTP transport is the required deployment mode - stdio-only servers are not exposed to this remote vector). … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | Signals are internally consistent and point to a genuine but scope-limited availability risk. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker who can reach the MCP server's HTTP endpoint sends a single POST to the JSON-RPC route with a multi-gigabyte body (or a chunked request with no/spoofed Content-Length), causing the worker to buffer and parse the whole payload and exhaust memory. Repeating this against each worker keeps the service crashing or OOM-restarting, denying availability to all users. … |
| Remediation | Vendor-released patch: upgrade the mcp gem to 0.23.0 or later, which enforces a 4 MiB default request-body cap (max_request_bytes) and a JSON nesting limit of 64; see GHSA-h669-8m4g-r2hc and the v0.23.0 release notes. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, audit all systems to identify mcp gem installations and immediately restrict network exposure to trusted sources only. …
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External POC / Exploit Code
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