Answer in brief
CVE-2026-116686 records a Medium severity (CVSS 6.5) vulnerability in Model Context Protocol Python SDK: Client fetched server-chosen $ref URLs while validating tool results against output schemas. The current sources do not mark it as known exploited. The current feed maps modelcontextprotocol/python-sdk (generic), mcp (pip), mcp (pip). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 6.5. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps modelcontextprotocol/python-sdk (generic), mcp (pip), mcp (pip). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| modelcontextprotocol/python-sdkgeneric | >=1.10.0 <1.30.0 || >=2.0.0 <2.2.0 | 1.30.0, 2.2.0 |
| mcppip | >=2.0.0,<2.2.0 | 2.2.0 |
| mcppip | >=1.10.0,<1.30.0 | 1.30.0 |
Published upstream
Oct 27, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Oct 27, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Oct 27, 2026
The Model Context Protocol Python SDK is the official Python SDK for Model Context Protocol servers and clients. From 1.10.0 until 1.30.0 and 2.2.0, ClientSession, ClientSessionGroup, and Client tool calls validate server-declared outputSchema documents with jsonschema's default resolver, causing an unresolved $ref value to fetch an HTTP, HTTPS, or file URL from the client's network and filesystem context. A server can trigger blind requests or local-file reads and can stall every session in the process because resolution runs synchronously on the event loop without a timeout. This issue is fixed in versions 1.30.0 and 2.2.0.
Quoted source text, attributed separately from HOL analysis.