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🛡️ CVE-2026-4270 — aws-api-mcp-server

🟡 CVSS 5.5 — Medium ✅ No Known Exploit CWE-424 NVD
5.5
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

AWS API MCP File Access Restriction Bypass

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.

How this vulnerability can be exploited

This issue can be reached with local access to the system, attack complexity is low, an attacker needs no privileges on the target. A user must be tricked into taking some action. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality high, integrity none, availability none.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N

  • Attack vector: Local — a local account, shell or session on the host is needed.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: Required — someone has to click, open or visit something.
  • Scope: Unchanged — the damage stays inside the vulnerable component.
  • Confidentiality impact: High — total loss, or loss the attacker controls.
  • Integrity impact: None.
  • Availability impact: None.

Weakness class

CVE-2026-4270 is classified as CWE-424: Improper Protection of Alternate Path. The product does not sufficiently protect all possible paths that a user can take to access restricted functionality or resources.

Affected software

CVE-2026-4270 is recorded against 2 packages.

  • aws-api-mcp-server (from 0.2.14 up to 1.3.9)
  • awslabs-aws-api-mcp-server (from 0.2.14 up to 1.3.9)

Timeline and source

Published on 16 March 2026 and last revised on 17 June 2026. No public exploit is currently recorded for this entry. Record sourced from NVD.

References

aws.amazon.com
pypi.org

Same weakness in other software

These advisories are the same class of weakness (CWE-424: Improper Protection of Alternate Path) in other software:

Details

Severity MEDIUM
CVSS Score 5.5
CVSS Vector CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
CWE CWE-424
Public Exploit ✅ No
Source NVD
Published 2026-03-16
Updated 2026-08-20
Modified 2026-06-17
Fix URL N/A

Affected Packages

Software From version Fixed in
aws-api-mcp-server 0.2.14 1.3.9
awslabs-aws-api-mcp-server 0.2.14 1.3.9

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