CVE-2026-125271

Custom MCP policies could miss operations an operator had restricted

AWS · AWS API MCP Server

First documented disclosure · Review checkpoint

Summary

The server normalized operation names inconsistently when matching its policy. Operations could run without the configured policy check or approval.

Severity and exploitation evidence

High · 8.5/10 · CVSS 4.0. Severity source.

Exploitation not established: The reviewed advisory does not report malicious exploitation.

Exploitation evidence source

Technical severity is not a measure of observed attacks or of risk to your deployment. Attempts, demonstrations, and successful compromise retain the qualifications in the source.

How the weakness works

The server normalized operation names inconsistently when matching its policy.

Conditions required

An MCP client invoked an operation covered by a denial or approval rule. The service identity needed permission for the underlying AWS action.

Potential impact

Operations could run without the configured policy check or approval.

Affected versions and configurations

0.2.13 through versions before 1.5.1.

Fix and mitigation status

1.5.1.

Practical next steps

Upgrade the server, including any derivative that carries the affected policy logic.

Operating lesson

Check the authority granted to the affected component against the operation a user expects.

Evidence and limits

The CVE record was published on 2026-11-10.

Sources