MCP Ruby SDK: Unbounded session retention in StreamableHTTPTransport allows memory exhaustion via initialize flood
Priority MEDIUM 63CWE-401Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- None · None · Low
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-401.
Summary
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.
Why it matters now
Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00367 30th percentileScored 2026-11-07
Fix Fixed ruby-sdk (modelcontextprotocol): 0.23.0mcp (RubyGems): 0.23.0
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- Poc
- Automatable
- Yes
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| MLflow | ruby-sdk | before 0.23.0 | 0.23.0 | Patch available | CNA |
| — | mcp (RubyGems) | before 0.23.0 | 0.23.0 | Patch available | GHSA-52jp-gj8w-j6xh |
- ruby-sdk VendorMLflow Affected before 0.23.0 Fixed in 0.23.0 Patch available CNA
- mcp (RubyGems) Vendor— Affected before 0.23.0 Fixed in 0.23.0 Patch available GHSA-52jp-gj8w-j6xh
Remediation
- Fix · CNA ruby-sdk (modelcontextprotocol) Fixed in 0.23.0
- Fix · GHSA-52jp-gj8w-j6xh mcp (RubyGems) Fixed in 0.23.0 Advisory →
Timeline
- 2026-10-02 Threatist record created from CVE-2026-67430
- 2026-10-03 Alias added: GHSA-52jp-gj8w-j6xh
References
Other 4
- https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-52jp-gj8w-j6xh
- https://github.com/modelcontextprotocol/ruby-sdk/commit/afb968c468c178c4d3294b423fcce250621692f4
- https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0
- https://github.com/modelcontextprotocol/ruby-sdk
More MLflow vulnerabilities
- TI-2026-46366 Server-side request forgery in mlflow KEVCVSS 3.1CRITICAL 9.3
- TI-2023-03518 Absolute Path Traversal in mlflow/mlflow CVSS 3.1CRITICAL 10.0
- TI-2023-01113 Path Traversal: '\..\filename' in mlflow/mlflow CVSS 3.1CRITICAL 9.8
- TI-2025-31759 Redis Lua Use-After-Free may lead to remote code execution CVSS 3.1CRITICAL 10.0
- TI-2026-81527 Code execution via scorer deserialization in MLflow servers CVSS 3.1CRITICAL 9.8
- TI-2025-14028 Command Injection in mlflow/mlflow CVSS 3.1CRITICAL 10.0
Sources
- CVE-2026-67430 · CVE Program
- CVE-2026-67430 · NVD
- FIRST EPSS
- GHSA-52jp-gj8w-j6xh · GitHub Advisory Database · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences