CVE-2026-4270

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 provides programmatic access to manage your AWS infrastructure while maintaining proper security controls.

This server acts as a bridge between AI assistants and AWS services, allowing you to create, update, and manage AWS resources across all available services. The server includes a configurable file access feature that controls how AWS CLI commands interact with the local file system. By default, file operations are restricted to a designated working directory (workdir), but this can be configured to allow unrestricted file system access (unrestricted) or to block all local file path arguments entirely (no-access).

Description: Improper Protection of Alternate Path exists in the no-access and workdir feature of the AWS API MCP Server versions >= 0.2.14 and < 1.3.9 on all platforms may allow the bypass of intended file access restriction and expose arbitrary local file contents in the MCP client application context.

To remediate this issue, users should upgrade to version 1.3.9.

CVE-2026-4270 has a CVSS score of 5.5 (Medium). The vector is requires local access, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.3.9); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-4270? CVE-2026-4270 is a medium-severity security vulnerability in awslabs.aws-api-mcp-server (pip), affecting versions >= 0.2.14, < 1.3.9. It is fixed in 1.3.9.
2. How severe is CVE-2026-4270? CVE-2026-4270 has a CVSS score of 5.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by CVE-2026-4270?
   • awslabs.aws-api-mcp-server (pip) (versions >= 0.2.14, < 1.3.9)
   • awslabs-aws-api-mcp-server (pip) (versions >= 0.2.14, < 1.3.9)
4. Is there a fix for CVE-2026-4270? Yes. CVE-2026-4270 is fixed in 1.3.9. Upgrade to this version or later.
5. Is CVE-2026-4270 exploitable, and should I be worried? Whether CVE-2026-4270 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-4270 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-4270?
   • Upgrade awslabs.aws-api-mcp-server to 1.3.9 or later
   • Upgrade awslabs-aws-api-mcp-server to 1.3.9 or later