GHSA-4wq9-grf3-qg2p · AI agents & MCP
NO FIX YET · SEE WHAT TO DO
The AWS API MCP Server normalized operation names incorrectly, so operations with consecutive capital letters never matched the operator's denyList or elicitList entries. An actor could run AWS API operations that the operator's security policy was meant to deny or require confirmation for.
first public Nov 10, 2026 · 1 source
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Teams that run the AWS API MCP Server with a custom security policy (denyList or elicitList) that lets AI assistants call AWS APIs. Forked or derivative copies of the code are also affected until patched. Servers on 1.5.1 or later, or without a custom policy, are not affected by this bypass.
Not affected if no-custom-security-policy, version-1.5.1-or-later
Who cares aws, aws-api-mcp-server, lab-disclosure, mcp
awslabs.aws-api-mcp-server version; affected versions are >= 0.2.13 and < 1.5.1.denyList or elicitList entries on the server.awslabs.aws-api-mcp-server upgrade to 1.5.1CVE-2026-125271 - AWS API MCP Server Security Policy Bypass via Incorrect Operation Name Normalization
Bulletin ID: 2026-176-AWS Scope: AWS Content Type: Important (requires attention) Publication Date: 11/10/2026 08:30 AM PST
Description:
AWS API MCP Server is an open source Model Context Protocol (MCP) server that customers run to let AI assistants manage their AWS accounts through AWS API calls.
We identified CVE-2026-125271, an issue in the custom security policy enforcement of AWS API MCP Server versions between 0.2.13 and 1.5.0. The server normalized operation names incorrectly before comparing them to the operator's security policy, so operations whose names contain consecutive capital letters never matched a correctly written denyList or elicitList entry. This might allow an actor to execute AWS API operations that the operator's security policy was configured to deny or require elicitation for.
Impacted versions: >= 0.2.13 AND < 1.5.1
Resolution:
This issue has been addressed in awslabs.aws-api-mcp-server version 1.5.1. We recommend upgrading to the latest version and ensuring any forked or derivative code is patched to incorporate the new fixes.
Workarounds:
There is no workaround other than upgrading.
References:
Acknowledgement:
We would like to thank Syed Anas Mohiuddin for collaborating on this issue through the coordinated vulnerability disclosure process.
Please email aws-security@amazon.com with any s ecurity questions or concerns.
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