The YosefHayim ebay-mcp server is affected by an environment variable injection vulnerability that may allow authenticated attackers to manipulate system configurations and potentially achieve remote code execution.

The vulnerability exists in the updateEnvFile function within src/auth/oauth.ts, which fails to neutralize special characters such as newlines or quotes when processing environment variables. An authenticated attacker can leverage the ebay_set_user_tokens tool to inject arbitrary environment variables into the local .env configuration file.

Successful exploitation of this vulnerability poses a severe risk to the integrity and availability of the affected system. By injecting malicious configuration settings, an attacker could alter application behavior, cause a denial of service, or potentially gain remote code execution, which would lead to a total compromise of the host environment. The CVSS score of 8.3 reflects the high impact on integrity and availability, necessitating immediate attention despite the requirement for authenticated access.

Immediate Action: As no official fix has been released, administrators should restrict access to the ebay-mcp server to trusted users only and monitor the .env file for unauthorized modifications.

Proactive Monitoring: Implement file integrity monitoring on the .env file to detect unexpected changes and review application logs for suspicious calls to the ebay_set_user_tokens tool.

Compensating Controls: Deploy a Web Application Firewall or similar access control mechanism to strictly limit interactions with the oauth.ts related endpoints and prevent unauthorized tool execution.

Public Exploit Available: Unknown

Given the potential for remote code execution and the lack of an available vendor patch, the risk associated with this vulnerability is significant. Organizations should isolate the affected instance from untrusted networks and implement strict authentication controls to prevent exploitation while awaiting a permanent fix.