CWE-782: Exposed IOCTL with Insufficient Access Control

What is Exposed IOCTL with Insufficient Access Control?

• Overview: An IOCTL (Input/Output Control) is a system call for device-specific input/output operations. This vulnerability occurs when an IOCTL with sensitive functionality is exposed without proper access control, allowing unauthorized users to invoke it.

• Exploitation Methods:

• Attackers can exploit this vulnerability by directly invoking the exposed IOCTL without any authentication or authorization checks.
• Common attack patterns include sending maliciously crafted data to the IOCTL to trigger unintended behavior or escalate privileges.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized access to privileged functionality, potentially leading to data leakage or system compromise.
• Potential cascading effects can involve privilege escalation, data corruption, or denial of service.
• Business impact may include loss of sensitive data, system downtime, reputational damage, and financial loss due to breaches.

• Prevention Guidelines:

• Specific code-level fixes involve implementing strict access control checks before allowing any IOCTL invocation, ensuring only authorized processes can access sensitive functionalities.
• Security best practices include conducting thorough input validation, ensuring least privilege access, and regularly auditing IOCTL implementations for security flaws.
• Recommended tools and frameworks include static analysis tools to detect insecure IOCTLs, and using operating system-provided mechanisms for access control, such as Discretionary Access Control (DAC) or Mandatory Access Control (MAC) policies.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: C, C++

Affected Technologies: Not specified

Vulnerable Code Example

#include <linux/ioctl.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/uaccess.h>

#define DEVICE_NAME "vulnerable_device"
#define IOCTL_CMD_1 _IOW('a', 'a', int32_t*)

static long device_ioctl(struct file *file, unsigned int cmd, unsigned long arg) {
    int32_t value = 0;

    switch (cmd) {
        case IOCTL_CMD_1:
            // Vulnerable: No access control checks
            // This allows any user to execute this IOCTL, potentially causing harm
            if (copy_from_user(&value, (int32_t*)arg, sizeof(value))) {
                return -EFAULT;
            }
            printk(KERN_INFO "Received value: %d\n", value);
            break;
        default:
            return -EINVAL;
    }
    return 0;
}

static struct file_operations fops = {
    .unlocked_ioctl = device_ioctl,
};

static int __init vulnerable_init(void) {
    // Device setup omitted for brevity
    return 0;
}

static void __exit vulnerable_exit(void) {
    // Cleanup omitted for brevity
}

module_init(vulnerable_init);
module_exit(vulnerable_exit);

MODULE_LICENSE("GPL");

Explanation

In the vulnerable code example, the device_ioctl function handles an IOCTL command without any access control checks. This means any user, regardless of their permissions, can execute the command, which can lead to unauthorized access or modification of device state.

How to fix Exposed IOCTL with Insufficient Access Control?

To fix the exposed IOCTL with insufficient access control, we need to implement proper access control checks to ensure that only authorized users can execute sensitive IOCTL commands. This can be achieved by checking the user credentials or process capabilities before allowing the execution of privileged IOCTL commands.

Specifically, the following steps should be implemented:

1. Check Process Capabilities: Use functions like capable() to check if the calling process has the necessary capabilities, such as CAP_SYS_ADMIN.
2. Return an Error for Unauthorized Access: If the access check fails, return an appropriate error code, such as -EPERM (operation not permitted).

Fixed Code Example

#include <linux/ioctl.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/uaccess.h>
#include <linux/capability.h>

#define DEVICE_NAME "secure_device"
#define IOCTL_CMD_1 _IOW('a', 'a', int32_t*)

static long device_ioctl(struct file *file, unsigned int cmd, unsigned long arg) {
    int32_t value = 0;

    switch (cmd) {
        case IOCTL_CMD_1:
            // Fixed: Implement access control checks
            if (!capable(CAP_SYS_ADMIN)) {
                printk(KERN_WARNING "Unauthorized access attempt\n");
                return -EPERM; // Return error if the user doesn't have necessary privileges
            }
            if (copy_from_user(&value, (int32_t*)arg, sizeof(value))) {
                return -EFAULT;
            }
            printk(KERN_INFO "Received value: %d\n", value);
            break;
        default:
            return -EINVAL;
    }
    return 0;
}

static struct file_operations fops = {
    .unlocked_ioctl = device_ioctl,
};

static int __init secure_init(void) {
    // Device setup omitted for brevity
    return 0;
}

static void __exit secure_exit(void) {
    // Cleanup omitted for brevity
}

module_init(secure_init);
module_exit(secure_exit);

MODULE_LICENSE("GPL");

Explanation

In the fixed code example, proper access control is enforced by using the capable() function to check if the calling process has the CAP_SYS_ADMIN capability before executing the IOCTL command. This ensures that only authorized users can perform potentially harmful operations, thus mitigating the security risk associated with CWE-782. The code now logs unauthorized access attempts and returns an appropriate error code to prevent unauthorized actions.