CVE-2026-116686
Description
A flaw was found in mcp. Client sessions validate server-declared schema documents using a default resolver that automatically retrieves external network and local filesystem references. A malicious server can exploit this flaw to cause a Denial of Service (DoS) by stalling client sessions synchronously or to trigger unauthorized local file reads and outbound network requests.
Statement
This vulnerability is rated as Moderate severity rather than Important because exploitation requires a client to interact with an untrusted or compromised Model Context Protocol (MCP) server, and any retrieved file content is not returned to the remote endpoint. In Red Hat environments integrating MCP client components, such as AI assistant services and tooling stacks, clients typically connect only to pre-approved or internal server instances. If an integration connects to an adversarial server, synchronous reference resolution can block the application event loop and cause a denial of service. Implementations functioning solely as MCP servers or communicating exclusively with trusted endpoints are unaffected.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 6.5 | N/A | 6.5 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | Required | N/A | Required |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | None | N/A | None |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
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