eBay API MCP Server is an open source local MCP server providing AI assistants with comprehensive access to eBays Sell APIs. All versions are vulnerable to Environment Variable Injection through the updateEnvFile function. 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. An attacker can inject arbitrary environment variables into the .env file. This could lead to configuration overwrites, Denial of Service, and potential RCE. There was no fix for this issue at the time of publication.
Weakness
One or more system settings or configuration elements can be externally controlled by a user.
Potential Mitigations
- Compartmentalize the system to have “safe” areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area.
- Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.
Related Attack Patterns
- https://cwe.mitre.org/data/definitions/13.html
- https://cwe.mitre.org/data/definitions/146.html
- https://cwe.mitre.org/data/definitions/176.html
- https://cwe.mitre.org/data/definitions/203.html
- https://cwe.mitre.org/data/definitions/270.html
- https://cwe.mitre.org/data/definitions/271.html
- https://cwe.mitre.org/data/definitions/579.html
- https://cwe.mitre.org/data/definitions/69.html
- https://cwe.mitre.org/data/definitions/76.html
- https://cwe.mitre.org/data/definitions/77.html