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AWS Vulnerability - Local File Inclusion Risk Exposed

VAVaronis Blog
CVE-2026-4270AWS MCP ServerLocal File InclusionVaronisAWS CLI
🎯

Basically, a flaw in AWS lets users read sensitive files they shouldn't access.

Quick Summary

A serious Local File Inclusion vulnerability in AWS Remote MCP Server has been discovered, allowing file access to authenticated users. This poses a risk of sensitive data exposure. AWS users must upgrade to the latest version to safeguard their systems.

The Flaw

Varonis Threat Labs has uncovered a Local File Inclusion (LFI) vulnerability in the AWS Remote MCP Server. This issue allows an authenticated user to read arbitrary files from the underlying operating system. The vulnerability can lead to attackers obtaining sensitive information, such as credentials, from the hosting server. This flaw exists despite the MCP server being configured with FileAccessMode=NO_ACCESS, indicating a serious oversight in security protocols.

The vulnerability is triggered by specific AWS commands that allow input from local files. When processed by the MCP server, these commands can unintentionally reveal information through error messages. Varonis successfully reproduced this behavior against the official public AWS MCP endpoint, highlighting the real-world risk associated with this issue.

What's at Risk

The LFI vulnerability effectively breaks the security boundary assumed by the FileAccessMode=NO_ACCESS setting. This allows for arbitrary file reads from the MCP server host, potentially exposing sensitive system files and secrets. The impact is significant because it not only affects self-hosted deployments but also extends to anyone using outdated versions of the AWS MCP server.

Organizations that fail to address this vulnerability risk disclosing critical information about their systems and configurations. This could lead to further exploitation by malicious actors who can leverage the exposed data for unauthorized access or attacks.

Patch Status

AWS has acknowledged the issue and addressed it in aws-api-mcp-server version 1.3.9, issuing CVE-2026-4270 as a formal identifier for the vulnerability. Users are strongly advised to upgrade to the latest version of the MCP server to mitigate the risks associated with this vulnerability. It is also crucial for organizations to ensure that any forked or derivative code is patched to incorporate these fixes.

The vulnerability has been present in all versions of the MCP server since 0.2.14, making it essential for all users to verify their current version and take appropriate action.

Immediate Actions

Organizations using the AWS Remote MCP Server should take immediate steps to protect their data. Here are three recommended actions:

  1. Upgrade to the latest version of the AWS MCP server to close the vulnerability.
  2. Review and audit any configurations that may expose sensitive data through CLI commands.
  3. Implement monitoring to detect any unauthorized access attempts or anomalies in server behavior.

By addressing this vulnerability promptly, organizations can significantly reduce their risk of data exposure and enhance their overall security posture against potential threats.

🔒 Pro insight: This LFI vulnerability exemplifies the risks of exposing CLI features in remote services, necessitating stringent security reviews.

Original article from

Varonis Blog · Coby Abrams

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