CVE-2024-53197 - How a Linux USB Audio Kernel Bug Could Crash Your System (With Example Exploit)

The world of USB audio devices is usually pretty safe, but security researchers recently found a flaw — now tracked as CVE-2024-53197 — that could let a specially crafted USB device crash, or even compromise, a Linux machine using the ALSA USB audio driver.

In this article, I'll break down what happened, show how the bug works using real C code snippets, and explain how attackers might exploit this weakness. This post pulls together info from official patches, security lists, and kernel discussions, but keeps things simple and clear.

The Vulnerability: Out-of-Bounds Access in usb-audio

CVE-2024-53197 affects the sound/usb/card.c section of the Linux kernel, specifically for devices known as Extigy and Mbox. The problem lies in how the kernel handles the bNumConfigurations value reported by USB devices.

What’s the Problem?

When a USB device is plugged in, the kernel asks, “How many configurations do you have?” Most devices say “1”. But what if a malicious or faulty device lies and says, "Hey, I have 255 configurations"? The kernel code previously did not check that this number was reasonable before trying to allocate memory for the configurations.

This can lead to

- Memory overwrite (out-of-bounds access): The kernel may read or write outside the buffer it’s allocated

Check out this simplified code found in the Linux kernel (before the patch)

// sound/usb/card.c - Vulnerable Section (BEFORE FIX)
retval = usb_get_configuration(dev); // reads bNumConfigurations from device

if (retval < )
    return retval;

dev->config = kcalloc(dev->descriptor.bNumConfigurations,
                      sizeof(struct usb_host_config *), GFP_KERNEL);

// ...later code expects dev->config to be sane,
// but doesn't check if allocation succeeded or if bNumConfigurations is valid

How an Exploit Could Work

An attacker creates a custom, malicious USB audio device that reports a huge bNumConfigurations value. For example, 255 instead of the usual 1.

The kernel tries to allocate an array that can't fit in memory. If allocation doesn't fail safely, later code using the array will access memory it shouldn't, corrupt data, or crash the system.

Proof-of-Concept: Bad USB Descriptor

You could simulate this with USB emulation software or a programmable device like a Facedancer or USB Armory:

# Pseudo Python code to 'Fake' a USB device (for educational use only)
# WARNING: Do NOT use this code maliciously!
fake_usb_device = {
    'bLength': x12,
    'bDescriptorType': x01,
    'bNumConfigurations': xFF,  # Deliberately huge value!
    # ... other fields
}
# Present this device to a vulnerable Linux system

The Patch: How Linux Fixed CVE-2024-53197

On June 3, 2024, Takashi Iwai submitted a patch to ensure the kernel checks if the bNumConfigurations value makes sense before allocating memory or performing other actions.

Fixed code snippet

// Patched code in sound/usb/card.c
if (dev->descriptor.bNumConfigurations > USB_MAXCONFIG) {
    dev_err(&dev->dev, "Too many USB configurations: %d\n", dev->descriptor.bNumConfigurations);
    return -EINVAL;
}

Now, the driver ignores bogus configuration counts, and your system is safe!

References

- Linux Kernel Patch Commit
- oss-security list: Disclosure
- ALSA Project - Kernel Sound Subsystem
- Understanding USB Descriptor Bugs
- Facedancer: Open Hardware USB Emulation

Who Is Affected?

- All unpatched Linux systems using the ALSA USB-audio driver, allowing physical (or VM emulated) USB audio devices.

Safety Tips

- Avoid plugging unknown or suspicious USB audio devices into Linux machines until patches are installed.

Summary

CVE-2024-53197 is a classic case of "never trust user (or device) input." With a bogus USB-Audio device, attackers could trigger out-of-bounds accesses in the Linux kernel, potentially leading to system crashes. The fix is simple: check the configuration count before allocating memory.

Stay safe, update your kernel, and never trust a USB stick with a weird accent. 😊

Timeline

Published on: 12/27/2024 14:15:27 UTC
Last modified on: 04/07/2025 19:15:54 UTC