EUVD-2026-50498
GHSA-52jp-gj8w-j6xh
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Unauthenticated network access with no complexity; memory exhaustion can crash the process entirely, warranting A:H over official A:L.
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:L
Lifecycle Timeline
3DescriptionCVE.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 does not expire sessions by default, so repeated initialize requests retain unbounded ServerSession objects and can exhaust process memory. This issue is fixed in version 0.23.0.
AnalysisAI
Unbounded session growth in MCP Ruby SDK's StreamableHTTPTransport allows unauthenticated remote attackers to exhaust server process memory by repeatedly sending initialize requests. Affected versions prior to 0.23.0 defaulted to no session expiry and no concurrent session cap, meaning each initialize request created a persistent ServerSession object that was never reclaimed without an explicit client DELETE. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | The target must be running a version of the mcp Ruby gem prior to 0.23.0 with MCP::Server::Transports::StreamableHTTPTransport in stateful mode (stateless: false, the default). … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS vector (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L) accurately reflects the network-accessible, zero-authentication, low-complexity attack surface, but the official A:L rating may understate impact: sustained initialize flooding can fully exhaust process memory and crash the Ruby process, which is closer to A:H behavior. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker sends a continuous stream of HTTP initialize requests to the StreamableHTTPTransport endpoint without ever issuing DELETE requests. Each request allocates a new ServerSession object retained indefinitely in the session hash. … |
| Remediation | Upgrade the mcp gem to version 0.23.0 or later; the fix is published at https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0. … Detailed patch versions, workarounds, and compensating controls in full report. |
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Session hijacking in the MCP Ruby SDK (mcp gem) before 0.23.0 lets an attacker who obtains a valid session ID issue tool
Uncontrolled memory allocation in the official Model Context Protocol Ruby SDK (mcp gem) before 0.23.0 lets an unauthent
DNS rebinding in MCP Ruby SDK's StreamableHTTPTransport (mcp gem, all versions prior to 0.23.0) exposes locally running
Uncontrolled memory growth in the MCP Ruby SDK (mcp gem) prior to 0.23.0 allows any peer process communicating via stdio
Same weakness CWE-401 – Memory Leak
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External POC / Exploit Code
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