Bulletin ID: 2026-152-AWS
Scope: AWS
Content Type: Important (requires attention)
Publication Date: 10/27/2026 11:00 AM PDT

Description:

The AWS API MCP Server is an open source Model Context Protocol (MCP) server that enables AI assistants to interact with AWS services and resources through AWS CLI commands. It can be configured to serve the streamable-http transport with OAuth authentication, validating a bearer token against an identity provider nominated by the operator. We identified CVE-2026-115413 in versions >=1.3.0 and <1.6.0, the server validates a token's signature, issuer and expiry, but not the claim identifying the application the token was issued for. A token that the nominated identity provider issued to another application in the same tenant is therefore accepted, which may allow AWS API calls to be made with the credentials configured on the host.

Impacted versions: >=1.3.0 AND <1.6.0

Resolution:

This issue has been addressed in awslabs.aws-api-mcp-server version 1.6.0. We recommend upgrading to the latest version and ensuring any forked or derivative code is patched to incorporate the new fixes. Operators using AUTH_TYPE=oauth should also set AUTH_AUDIENCE, or AUTH_CLIENT_ID for identity providers whose access tokens carry no audience claim, such as Amazon Cognito.

Workarounds:

Operators who cannot upgrade immediately can use the default stdio transport rather than the streamable-http transport.

References:

• CVE-2026-115413
• GHSA-4prq-p2x5-w9fh

Acknowledgement:

We would like to thank Yuval Elbar (@YuvalElbar6) for collaborating on this issue through the coordinated vulnerability disclosure process.

Please email aws-security@amazon.com with any security questions or concerns.