Summary
mac-shell-mcp contains an OS command injection vulnerability in its command execution interface, allowing shell metacharacters to bypass intended command restrictions. An attacker or malicious prompt may cause forbidden commands to run with the server user's privileges when crafted arguments reach the shell.
mac-shell-mcp contains an OS command injection vulnerability in its command execution interface, allowing shell metacharacters to bypass intended command restrictions. An attacker or malicious prompt may cause forbidden commands to run with the server user's privileges when crafted arguments reach the shell.
Affected context
The vulnerability affects mac-shell-mcp deployments that expose the execute_command functionality to MCP clients or prompt-driven workflows and pass user-controlled arguments to a shell. It becomes risky when command allowlisting validates only the base command while failing to constrain or safely handle argument content.
The vulnerability affects mac-shell-mcp deployments that expose the execute_command functionality to MCP clients or prompt-driven workflows and pass user-controlled arguments to a shell. It becomes risky when command allowlisting validates only the base command while failing to constrain or safely handle argument content.
Exploit preconditions
- Attack surface: The MCP command-execution interface
- Required access: Ability to invoke the relevant MCP tool, directly or through an untrusted prompt or client
- Trigger point: Processing execute_command arguments before command execution
- Why exploitation is possible: Shell metacharacters in arguments can alter command interpretation and bypass restrictions applied only to nominally approved commands
- Attack surface: The MCP command-execution interface
- Required access: Ability to invoke the relevant MCP tool, directly or through an untrusted prompt or client
- Trigger point: Processing execute_command arguments before command execution
- Why exploitation is possible: Shell metacharacters in arguments can alter command interpretation and bypass restrictions applied only to nominally approved commands
Why this happens
The underlying bug is improper neutralization of special elements used in an OS command. The application treats arguments as data for an approved command but passes them through a shell interpretation path without reliably separating executable structure from user-controlled values. This behavior maps to CWE-78, OS Command Injection, because attacker-controlled input can influence the commands executed by the operating system.
The underlying bug is improper neutralization of special elements used in an OS command. The application treats arguments as data for an approved command but passes them through a shell interpretation path without reliably separating executable structure from user-controlled values. This behavior maps to CWE-78, OS Command Injection, because attacker-controlled input can influence the commands executed by the operating system.
Potential impact
- An attacker may execute arbitrary operating-system commands as the server user.
- The attacker could read, modify, or delete files accessible to that account.
- Application credentials, tokens, or configuration data may be exposed.
- The vulnerable service could be used for lateral movement or further system compromise.
- An attacker may execute arbitrary operating-system commands as the server user.
- The attacker could read, modify, or delete files accessible to that account.
- Application credentials, tokens, or configuration data may be exposed.
- The vulnerable service could be used for lateral movement or further system compromise.
General mitigation guidance
Mitigation generally focuses on avoiding shell interpretation and reducing trust
in command arguments.
Common defensive patterns include:
- Prefer direct process execution APIs that pass a fixed executable and structured argument list without invoking a shell.
- Enforce a strict allowlist for complete commands and permitted argument schemas, rather than validating only command names.
- Treat MCP tool inputs and prompt-derived values as untrusted, and apply type, length, character, and semantic validation.
- Run the service with a dedicated least-privileged account, restricted filesystem access, and minimal network permissions.
- Require explicit authorization for sensitive operations and isolate command-execution workers where practical.
Mitigation generally focuses on avoiding shell interpretation and reducing trust
in command arguments.
Common defensive patterns include:
- Prefer direct process execution APIs that pass a fixed executable and structured argument list without invoking a shell.
- Enforce a strict allowlist for complete commands and permitted argument schemas, rather than validating only command names.
- Treat MCP tool inputs and prompt-derived values as untrusted, and apply type, length, character, and semantic validation.
- Run the service with a dedicated least-privileged account, restricted filesystem access, and minimal network permissions.
- Require explicit authorization for sensitive operations and isolate command-execution workers where practical.
How teams detect issues like this
Organizations can look for this weakness through:
- Static analysis rules for shell-spawning APIs, command concatenation, and interpolated user input.
- Code review checks for allowlists that inspect only the executable while permitting unrestricted arguments.
- Tests that submit shell-control characters and verify that they remain inert or are rejected.
- Runtime monitoring for unexpected child processes, command interpreters, or unusual file and network activity from the MCP service.
- Policy enforcement requiring direct, non-shell process execution for application-controlled commands.
Automated code review and software composition analysis tools may help identify related patterns, but should be supplemented with targeted security testing.
Organizations can look for this weakness through:
- Static analysis rules for shell-spawning APIs, command concatenation, and interpolated user input.
- Code review checks for allowlists that inspect only the executable while permitting unrestricted arguments.
- Tests that submit shell-control characters and verify that they remain inert or are rejected.
- Runtime monitoring for unexpected child processes, command interpreters, or unusual file and network activity from the MCP service.
- Policy enforcement requiring direct, non-shell process execution for application-controlled commands.
Automated code review and software composition analysis tools may help identify related patterns, but should be supplemented with targeted security testing.
