Path Traversal in LinuxCNC rtapi_app

Executive Summary

The vulnerability exists in the rtapi_app module of LinuxCNC before version 2.9.9. This module is installed with SUID root privileges and loads shared library modules using a user-supplied module name. Because the module name is not properly validated, an unprivileged local user can exploit path traversal by including characters like slashes ("/") or ".." in the module name. This allows the user to load an arbitrary shared library with elevated privileges, resulting in local privilege escalation to root.

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Impact Analysis

This vulnerability can allow an unprivileged local user to escalate their privileges to root on the affected system. By exploiting the insufficient validation of module names, an attacker can load arbitrary shared libraries with root privileges. This can lead to full system compromise, unauthorized access to sensitive data, and the ability to execute arbitrary code with the highest system privileges.

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Detection Guidance

This vulnerability involves the rtapi_app binary in LinuxCNC being installed with SUID root and loading shared libraries via user-supplied module names without proper validation.

To detect if your system is vulnerable, you can check if the rtapi_app binary is installed with SUID root permissions.

• Run the command: ls -l $(which rtapi_app) # to check if the binary has the SUID bit set (look for an 's' in the permissions, e.g., -rwsr-xr-x)
• Check the version of LinuxCNC installed to see if it is before 2.9.9, which is vulnerable.
• You can also audit system logs or monitor for unusual usage of rtapi_app or attempts to load modules with suspicious names containing slashes or '..' sequences.

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Mitigation Strategies

The primary mitigation is to update LinuxCNC to version 2.9.9 or later, where input sanitization for module names in rtapi_app has been implemented.

This update prevents module names containing slashes ("/") or the substring ".." from being loaded, blocking path traversal attacks.

If immediate update is not possible, consider removing the SUID bit from the rtapi_app binary to prevent privilege escalation, though this may impact functionality.

• Update LinuxCNC to version 2.9.9 or later.
• Remove SUID bit temporarily: sudo chmod u-s $(which rtapi_app)
• Monitor and restrict local user access to the system to prevent exploitation.

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Compliance Impact

The vulnerability allows local privilege escalation to root by exploiting insufficient validation of user-supplied module names in the rtapi_app component of LinuxCNC. This could potentially lead to unauthorized access or control over the affected system.

Such unauthorized privilege escalation and potential system compromise may impact compliance with standards and regulations like GDPR and HIPAA, which require protection of sensitive data and secure system access controls.

However, the provided information does not explicitly describe the direct effects of this vulnerability on compliance with these standards or any specific regulatory requirements.

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