---
id: "CVE-2026-115413"
kind: "vulnerability"
aliases: ["CVE-2026-115413"]
title: "Missing token audience validation in the OAuth authentication mode of AWS API MCP Server before version 1.6.0 might\u2026"
severity: "high"
cvss: 7.8
epss: null
exploited: false
status: "open"
category: "ai-tooling"
products: []
ecosystems: []
tags: ["ai-agents", "ai-tooling", "aws", "lab-disclosure", "mcp", "python", "self-hosted"]
not_affected_if: ["auth-not-oauth", "stdio-transport", "versions-outside-1.3.0-to-1.6.0"]
published_at: "2026-10-27T00:00:00+00:00"
first_seen_at: "2026-10-27T18:39:55+00:00"
updated_at: "2026-10-27T19:33:18+00:00"
sources: [{"source": "lab", "url": "https://aws.amazon.com/security/security-bulletins/rss/2026-152-aws/", "first_seen_at": "2026-10-27T18:39:55+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-115413", "first_seen_at": "2026-10-27T19:33:18+00:00"}]
---

# Missing token audience validation in the OAuth authentication mode of AWS API MCP Server before version 1.6.0 might…

The AWS API MCP Server in streamable-http mode with OAuth does not check the audience claim of bearer tokens, so a token issued by the same identity provider to a different application in the same tenant is accepted. An attacker holding such a token can make AWS API calls using the credentials configured on the host.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Run `pip show awslabs.aws-api-mcp-server` or check the installed package version; affected versions are >=1.3.0 and <1.6.0
- Check whether `AUTH_TYPE` is set to `oauth` and whether the server runs with the streamable-http transport
- Check whether `AUTH_AUDIENCE` or `AUTH_CLIENT_ID` is set

## Fix

- Upgrade awslabs.aws-api-mcp-server to `1.6.0` or later
- With `AUTH_TYPE=oauth`, set `AUTH_AUDIENCE`, or `AUTH_CLIENT_ID` for identity providers such as Amazon Cognito whose access tokens carry no audience claim
- Until upgraded, use the default stdio transport instead of streamable-http
- Patch any forked or derivative code with the new fixes

## Timeline

- 2026-10-27T18:39:55+00:00 lab https://aws.amazon.com/security/security-bulletins/rss/2026-152-aws/ — AWS: CVE-2026-115413 - AWS API MCP Server OAuth token audience validation bypass
- 2026-10-27T19:33:18+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-115413

## Documents

- [advisory] AWS: CVE-2026-115413 - AWS API MCP Server OAuth token audience validation bypass https://aws.amazon.com/security/security-bulletins/rss/2026-152-aws/

## From the sources

CVE-2026-115413 - AWS API MCP Server OAuth token audience validation bypass

### CVE-2026-115413 - AWS API MCP Server OAuth token audience validation bypass

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.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_