CVE-2023-28328: NULL Pointer Dereference Vulnerability in the Linux Kernel's az6027 Driver

A recently discovered vulnerability (CVE-2023-28328) in the Linux Kernel has shown that a NULL pointer dereference flaw exists in the az6027 driver, which is located in the drivers/media/usb/dvb-usb/az6027.c file. This vulnerability could potentially allow a local user to crash the system or cause a denial of service. This post will delve into the specifics of this vulnerability, provide code snippets to illustrate the problem, and offer links to original references for further information.

Vulnerability Details

The NULL pointer dereference flaw in the az6027 driver stems from improper checking of user space messages before they are transferred to the device. This means that an attacker who has local access to the machine could potentially exploit this vulnerability by sending a malicious message from user space. This could then lead to a system crash or denial of service, as the device becomes unable to function correctly.

Code Snippet

The following code snippet from the az6027 driver (located in drivers/media/usb/dvb-usb/az6027.c) demonstrates the issue:

static int az6027_recv_bulk(struct az6027_device_state *st, u8 *buf, size_t len)
{
	int ret;
	struct urb *urb;

	if (len > 4096)
		return -EIO;

	urb = usb_alloc_urb(, GFP_KERNEL);
	if (!urb)
		return -ENOMEM;

	usb_fill_bulk_urb(urb, st->udev, usb_rcvbulkpipe(st->udev, x81),
			  buf, len, az6027_read_bulk_completion, NULL);

	ret = usb_submit_urb(urb, GFP_KERNEL);
	if (ret)
		dev_err(&st->udev->dev, "recv bulk failed, urb %p, err %d\n",
			urb, ret);

	usb_free_urb(urb);
	return ret;
}

As shown in the snippet, the az6027_recv_bulk function makes no checks for NULL pointers before accessing the buf parameter.

Exploit Details

An attacker could potentially exploit this flaw by sending a malicious message to the device through user space. The following steps outline the basic process an attacker might use to exploit this vulnerability:

1. Gain local access to the target machine. This can be done by obtaining a user account through methods such as phishing, social engineering, or password attacks.

Craft a malicious message that contains a NULL pointer.

3. Send the message to the target device. This will pass the NULL pointer to the az6027_recv_bulk function, causing a dereference of the NULL pointer.
4. Observe the system crash or enter a state of denial of service due to improper handling of the NULL pointer.

Original References

- Linux Kernel Mailing List - NULL pointer dereference in the az6027 driver
- National Vulnerability Database - CVE-2023-28328

Conclusion

In summary, CVE-2023-28328 is a notable vulnerability in the Linux Kernel's az6027 driver, allowing for potential system crashes or denial of service if exploited by a local user. It's crucial for developers and system administrators to keep an eye on security updates and apply patches as they become available. Staying up to date on security developments helps ensure that systems are as resilient as possible to potential threats.

Timeline

Published on: 04/19/2023 23:15:00 UTC
Last modified on: 05/03/2023 14:15:00 UTC