A high-severity command injection vulnerability in MladenSU cli-mcp-server allows unauthenticated attackers to bypass security controls and execute arbitrary system commands.

The application fails to properly neutralize shell substitution characters (such as $() or backticks) within the _validate_command_with_operators function. This flaw permits unauthenticated attackers to execute arbitrary system commands that are not explicitly defined in the allowed command list, provided the ALLOW_SHELL_OPERATORS configuration is enabled.

Successful exploitation of this vulnerability allows for remote code execution on the host system, potentially leading to a full compromise of the application environment. Given the CVSS score of 8.1, this represents a significant risk to data confidentiality and system integrity. An attacker could leverage this access to exfiltrate sensitive information, modify system configurations, or deploy further malicious payloads, resulting in severe operational disruption.

Immediate Action: Disable the ALLOW_SHELL_OPERATORS configuration setting immediately if it is currently in use, as this is the primary vector for the bypass.

Proactive Monitoring: Review system and application logs for unexpected shell execution patterns or command strings containing shell substitution syntax like backticks or $().

Compensating Controls: Deploy a Web Application Firewall (WAF) or an equivalent input validation layer to filter and reject requests containing shell-specific metacharacters before they reach the backend service.

Public Exploit Available: Unknown.

The vulnerability poses a substantial risk due to the potential for unauthenticated remote code execution. Administrators should prioritize disabling the vulnerable configuration setting immediately and monitor for any anomalous execution attempts. Until an official patch is provided by the vendor, limiting the surface area of the application via network segmentation or WAF rules is strongly advised to prevent exploitation.