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Medium, CVSS 6.8amended

AWS API MCP File Access Restriction Bypass

CVE-2026-4270GHSA-2cpp-j2fc-qhp7

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (awslabs-aws-api-mcp-server 1.3.9), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
6.8 · CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N · score source
EPSS
  • CVE-2026-4270: 0.14% estimated exploitation activity in the next 30 days; percentile 3.04 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

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…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-2cpp-j2fc-qhp7

  2. Revision 2 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 1 · created ·

    Published from osv record GHSA-2cpp-j2fc-qhp7

Agent brief

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# Patch Next advisory brief: CVE-2026-4270

Advisory: AWS API MCP File Access Restriction Bypass
IDs: CVE-2026-4270, GHSA-2cpp-j2fc-qhp7
Record: https://patchnext.com/advisories/cve-2026-4270 (revision 3, source checked 26 Oct 2026, 13:45 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: awslabs-aws-api-mcp-server 1.3.9. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI awslabs-aws-api-mcp-server: affected >= 0.2.14, < 1.3.9; >= 0.2.14, < 1.3.9; fixed in 1.3.9

## Suggested inspection (read-only)
- `python -m pip show awslabs-aws-api-mcp-server`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on awslabs-aws-api-mcp-server.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-2cpp-j2fc-qhp7 (OSV record GHSA-2cpp-j2fc-qhp7 lists affected ranges: PyPI awslabs-aws-api-mcp-server >=0.2.14 <1.3.9 (fixed))
- Verified: https://github.com/advisories/GHSA-2cpp-j2fc-qhp7 (GitHub-reviewed advisory GHSA-2cpp-j2fc-qhp7 lists affected ranges: PyPI awslabs-aws-api-mcp-server >=0.2.14 =0.2.14 <1.3.9)

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