---
id: "CVE-2026-125271"
page: "https://infrastack.ai/live/CVE-2026-125271"
kind: "vulnerability"
aliases: ["CVE-2026-125271"]
title: "Incorrect normalization of operation names in the custom security policy enforcement in awslabs aws-api-mcp-server\u2026"
severity: "high"
cvss: 8.5
epss: null
exploited: false
status: "open"
category: "ai-tooling"
products: []
ecosystems: []
tags: ["ai-tooling", "aws", "aws-api-mcp-server", "lab-disclosure", "mcp", "self-hosted"]
not_affected_if: ["no-custom-security-policy", "version-1.5.1-or-later"]
published_at: "2026-11-10T17:17:28+00:00"
first_seen_at: "2026-11-10T17:00:47+00:00"
updated_at: "2026-11-10T17:22:41+00:00"
sources: [{"source": "lab", "url": "https://aws.amazon.com/security/security-bulletins/2026-176-aws/", "first_seen_at": "2026-11-10T17:00:47+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-125271", "first_seen_at": "2026-11-10T17:22:41+00:00"}]
exploit_sources: []
---

# Incorrect normalization of operation names in the custom security policy enforcement in awslabs aws-api-mcp-server…

Link for people: https://infrastack.ai/live/CVE-2026-125271 (this .md is for agents)

AWS API MCP Server normalizes operation names incorrectly, so names with consecutive capital letters never match a correctly written denyList or elicitList entry. An attacker can run AWS API operations the operator's security policy was meant to block or require confirmation for.

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

## How to check

- Find the installed version of awslabs.aws-api-mcp-server and check whether it is `>= 0.2.13` and `< 1.5.1`.
- Check whether the server enforces a custom security policy with a denyList or elicitList.

## Fix

- awslabs.aws-api-mcp-server: upgrade to `1.5.1`, and patch any forked or derivative code.

## Timeline

- 2026-11-10T17:00:47+00:00 lab https://aws.amazon.com/security/security-bulletins/2026-176-aws/ — AWS: CVE-2026-125271 - AWS API MCP Server Security Policy Bypass via Incorrect Operation Name Normalization
- 2026-11-10T17:22:41+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-125271

## Documents

- [advisory] AWS: CVE-2026-125271 - AWS API MCP Server Security Policy Bypass via Incorrect Operation Name Normalization https://aws.amazon.com/security/security-bulletins/2026-176-aws/
- [advisory] Vendor advisory: github.com https://github.com/awslabs/mcp/security/advisories/GHSA-4wq9-grf3-qg2p
- [mentions] AWS Security Bulletins: CVE-2026-125271 - AWS API MCP Server Security Policy Bypass via Incorrect Operation Name Normalization https://aws.amazon.com/security/security-bulletins/rss/2026-176-aws/

## From the sources

CVE-2026-125271 - AWS API MCP Server Security Policy Bypass via Incorrect Operation Name Normalization

### CVE-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:

- CVE-2026-125271
- GHSA-4wq9-grf3-qg2p

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.

---

_Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai_