CVE-2026-4270 AWS API MCP File Access Restriction Bypass
An attacker can bypass file access restrictions to read arbitrary local files via the AWS API MCP Server.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-4270?
CVE-2026-4270 is a medium-severity path traversal vulnerability in AWS API MCP Server, published on 16 Mar 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Official 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.
Weakness: CWE-424
Which versions are affected by CVE-2026-4270?
4 open source packages ship an affected version, including awslabs-aws-api-mcp-server and awslabs.aws-api-mcp-server. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
awslabs-aws-api-mcp-server PyPI | From 0.2.14 | 1.3.9 |
awslabs-aws-api-mcp-server PyPI | From 0.2.14 | 1.3.9 |
awslabs-aws-api-mcp-server PyPI | From 0.2.14 | 1.3.9 |
awslabs.aws-api-mcp-server PyPI | From 0.2.14 | 1.3.9 |
Products include Amazon Aws Api Mcp Server.
How do I fix CVE-2026-4270?
Upgrade awslabs-aws-api-mcp-server to 1.3.9 or later.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is CVE-2026-4270 being exploited?
There is no known exploitation of CVE-2026-4270 in the wild and no public exploit code.
Sources
Also known as GHSA-2cpp-j2fc-qhp7, PYSEC-2026-162.