CVE-2026-4270: AWS API MCP Server file access bypass in no-access and workdir features

CVE-2026-4270 · Severity: high · CVSS 5.5 · Published 2026-03-16

The AWS API MCP Server is a tool that allows AI assistants to manage AWS resources using standard command-line tools. A security flaw in how the server handles file paths could allow an attacker to bypass directory restrictions and access sensitive local files on the system where the server is running. This could lead to the exposure of private data or configuration files to the AI assistant's context.

Technologies: Amazon AWS, Aws-Api-Mcp-Server. Vendors: Amazon, AWS, PyPI.

Quick answers

Is CVE-2026-4270 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-4270 being exploited in the wild.
How severe is CVE-2026-4270?
High severity, with a CVSS score of 5.5, published 16 March 2026.
Which products and versions are affected?
Aws-Api-Mcp-Server >= 0.2.14, < 1.3.9; awslabs.aws-api-mcp-server (PyPI) ECOSYSTEM:introduced=0.2.14,fixed=1.3.9.
Is there a fix for CVE-2026-4270?
Yes. awslabs.aws-api-mcp-server (PyPI): upgrade to 1.3.9 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-4270 attacked?
It is attacked with local access, in a software library.
Am I affected by CVE-2026-4270?
Check whether you run Amazon AWS, Aws-Api-Mcp-Server or awslabs.aws-api-mcp-server (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • awslabs.aws-api-mcp-server (PyPI): upgrade to 1.3.9 or later
    pip install "awslabs.aws-api-mcp-server>=1.3.9"

Technical details

A vulnerability classified as Improper Protection of Alternate Path (CWE-424) exists in the AWS API MCP Server's 'no-access' and 'workdir' configurations. The root cause is insufficient validation of file path arguments passed to AWS CLI commands through the MCP bridge. An attacker can exploit this by providing specially crafted paths to bypass intended directory isolation, allowing the retrieval of arbitrary local file contents within the application context. Exploitation requires local access and some level of user interaction (passive). The issue is resolved in version 1.3.9.

Affected products

  • AWS aws-api-mcp-server >= 0.2.14, < 1.3.9

Identifiers

  • CVE-2026-4270
  • GHSA-2cpp-j2fc-qhp7
  • PYSEC-2026-162

Timeline

  • 2026-03-16: disclosed
  • 2026-03-16: patched: Version 1.3.9 released
  • 2026-03-17: advisory

References

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