GHSA-5w57-2ccq-8w95: Node.js Sandbox MCP Server vulnerability can lead to Sandbox Escape via Command Injection
SummaryA command injection vulnerability exists in the `node-code-sandbox-mcp` MCP Server. The vulnerability is caused by the unsanitized use of input parameters within a call to `child_process.execSync`, enabling an attacker to inject arbitrary system commands. Successful exploitation can lead to remote code execution under the server process's privileges on the host machine, bypassing the sandbox protection of running code inside docker.The server constructs and executes shell commands using unvalidated user input directly within command-line strings. This introduces the possibility of shell metacharacter injection (`|`, `>`, `&&`, etc.).DetailsThe MCP Server exposes tools to run code inside a docker container.  An MCP Client can be instructed to execute additional actions for example via indirect prompt injection when asked to generate code that read a file. Below some example of vulnerable code and different ways to test this vulnerability including a real example of indirect prompt injection that can lead to arbitrary command injection (bypassing sandboxing).Vulnerable codeThe following snippet illustrates the vulnerable code pattern used in the MCP Server’s tooling. **Note**: These is only one instance, but similar patterns may exist elsewhere in the codebase.PoCSetupdownload a docker image and create folder to store a (malicious) fileRealistic Example - Indirect prompt injection via file contentin the `~/shared` directory, create a file named `test.txt` with the following content to simulate untrusted content that should be processed inside the container:Verify the file `/tmp/TEST`1 does **not** exist (on the host machine):setup your client IDE (replace `/path/to/shared` with the folder where `test.txt` is saved)open the chat and enter the following prompt (it's an example)run the `run_js_epehemeral` tool. The request will look like the following (i.e js code that reads the file and prints the output):Observe that the response will contain the file content but will also trigger the `sandbox_stop` tool execution with a malicious payload that can lead to command injection on the host machinerun the `sandbox_stop` tool (if you have auto run functionality enabled this will be executed without user interaction)Result:Confirm that the injected command executed on the host machine (not inside the container):Another example (instead of reading a local file) would involve requesting the creation of JavaScript code that interacts with untrusted resources—such as fetching remote data or installing packages. In this case, I used a local file to simplify the PoC.Using MCP InspectorOpen the MCP Inspector:In MCP Inspector:set transport type: `STDIO`set the `command` to `npx`set the arguments to `node-code-sandbox-mcp@latest`Add environment variable: `FILES_DIR=/tmp/data`click Connectgo to the **Tools** tab and click **List Tools**select the `sandbox_stop` toolVerify the file `/tmp/TEST` does **not** exist:In the **container_id** field, input:Click **Run Tool**Observe the request being sent:Response:Confirm that the injected command executed:RemediationTo mitigate this vulnerability, I suggest to avoid using `child_process.execSync` with untrusted input. Instead, use a safer API such as [`child_process.execFileSync`](https://nodejs.org/api/child_process.html#child_processexecfilesyncfile-args-options), which allows you to pass arguments as a separate array — avoiding shell interpretation entirely.ImpactCommand Injection / Remote Code Execution (RCE) / Sandbox escapeReferenceshttps://equixly.com/blog/2025/03/29/mcp-server-new-security-nightmare/https://invariantlabs.ai/blog/mcp-github-vulnerability
CVSS v3.1: 7.5