CVE-2026-1166866.5MediumCWE-918

CVE-2026-116686: Model Context Protocol Python SDK: Client fetched server-chosen $ref URLs while validating tool results against output schemas

modelcontextprotocol · python-sdk

Affected: modelcontextprotocol python-sdk · Exploitation: unlikely (under 1%)

Not in CyberSIXT coverage yet: no article names this CVE. This page shows the public record.

0.3%probability of exploitation in the next 30 days

27th percentile

050100

Higher than 27% of scored CVEs

6.5MediumCVSS 3.1

LowMediumHighCrit.

DescriptionCVE.org

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.

Affected products1

From the CVE record. A product or version that is not listed is unknown, not unaffected.

modelcontextprotocol · python-sdk>= 1.10.0, < 1.30.0; >= 2.0.0, < 2.2.0

On the Atlas

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Exploitation: Unlikely (under 1%). EPSS under 1%, or no score yet.
CISA KEV: Not listed
Public check: No public nuclei template
Weakness: Server-Side Request Forgery
Vendor: modelcontextprotocol
Published: October 2026
Band: Unlikely (under 1%), October 2026

CoverageNo articles yet

No CyberSIXT article names CVE-2026-116686 yet, so there is no coverage timeline, action brief or change log for it. Everything on this page comes from the public CVE record, CISA KEV, EPSS and the nuclei template index. Search the archive or see the CVEs in the news.