eBay API MCP Server Affected by Environment Variable Injection

The ebay_set_user_tokens tool allows updating the .env file with new tokens. The updateEnvFile function in src/auth/oauth.ts blindly appends or replaces values without validating them for newlines or quotes. This allows an attacker to inject arbitrary environment variables into the configuration file.

Impact

An attacker can inject arbitrary environment variables into the .env file. This could lead to:

• Configuration Overwrites: Attackers can overwrite critical settings like EBAY_REDIRECT_URI to hijack OAuth flows.
• Denial of Service: Injecting invalid configuration can prevent the server from starting.
• Potential RCE: In some environments, controlling environment variables (like NODE_OPTIONS) can lead to Remote Code Execution.

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