CVE-2022-3903 is a security flaw found in the Linux kernel’s Infrared Transceiver USB driver. If you haven’t paid much attention to obscure device drivers before, this case will change your mind! By simply plugging in a malicious USB infrared device, someone could make your Linux system run out of resources or even crash altogether.

In this post, I’ll break down what went wrong, how this vulnerability can be abused, and walk through a simplified code example for educational purposes. All links and references are provided at the end. Let's keep things straightforward, so even if you’re not a low-level Linux developer, you’ll get the gist.

What’s CVE-2022-3903?

CVE-2022-3903 is described as an “incorrect read request” flaw in the Linux kernel’s IRCOMM USB (Infrared Communications) driver. In simple words:

Who is affected? Any Linux computer using the kernel with the vulnerable driver enabled.

- Trigger: Plugging in a specially crafted (malicious) USB device that claims to be an infrared transceiver.
- Impact: From making your computer very slow (resource starvation) to completely freezing or crashing (Denial of Service).

Why Does This Happen?

Let’s look at a high-level view. When Linux detects a new USB infrared device, its driver talks to the device using standardized requests. In the vulnerable code, the driver doesn’t properly check the input parameters from the device. If the device responds with unexpected (or malicious) data, the code tries to read more data than it should.

System hang or crash.

The attacker doesn’t need to be root. Just being able to plug in a USB device is enough—a real concern for public computers, servers, etc.

A Look at the Vulnerable Code

Here’s a simplified version of where things went wrong (based on the kernel patch):

// Function in drivers/usb/serial/ir-usb.c
static void ir_usb_read_bulk_callback(struct urb *urb)
{
    struct ir_usb_cb *cb = urb->context;
    int actual_length = urb->actual_length;

    // BEFORE PATCH:
    memcpy(cb->buffer, urb->transfer_buffer, actual_length); // No bound check!

    // AFTER PATCH:
    if (actual_length > sizeof(cb->buffer)) {
        // Prevent overflow
        actual_length = sizeof(cb->buffer);
    }
    memcpy(cb->buffer, urb->transfer_buffer, actual_length);
}

What’s the big deal? If the USB device says "Here’s 10,000 bytes of data," the old code would trust that and just copy it, even if the buffer is only, say, 512 bytes. This could corrupt memory or use up all available RAM if the process keeps repeating.

How Can an Attacker Exploit This?

1. Build or Modify a USB Device: An attacker could use a programmable USB device (like a USB rubber ducky, or a microcontroller with USB support) to pretend to be an Infrared transceiver.
2. Send Malicious Data: When plugged in, this device sends oversized or crafted responses to the driver’s read requests.
3. Driver Fails to Check: The kernel driver trusts the device and blindly allocates or copies the data.
4. Result: The system can run out of memory, slow to a crawl (resource starvation), or completely crash (Denial of Service).

USB Attack Example

Suppose you use a USB framework like GreatFET One or even an Arduino with custom USB firmware. By sending large data during initialization, you trigger the flaw. Here’s a conceptual Python snippet using PyUSB—purely illustrative:

import usb.core

dev = usb.core.find(idVendor=xYOUR_VENDOR, idProduct=xYOUR_PRODUCT)
if dev is None:
    raise ValueError('Device not found')
    
# Send oversized data in response
large_data = bytes([xAA] * 10000)  # 10,000 bytes (much larger than expected)
dev.write(ENDPOINT, large_data)

*Note: Practical exploitation requires writing the device firmware, since host-side PyUSB can't spoof as a device. But the idea is to return super-sized data when the driver expects a small packet.*

Mitigation & Patch

The fix is simple: check the amount of data before copying. The Linux kernel team patched the driver so that it will never copy more data than it can handle. Check your distributions for kernel version updates. If you use USB IR adapters, update ASAP.

Patch reference:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e7494e34af8693736502b8a9e4c1c8e6321e7b30

Example

sudo modprobe -r ir-usb
echo "blacklist ir-usb" | sudo tee /etc/modprobe.d/ir-usb.conf

Final Thoughts

This vulnerability is a classic example of why drivers for "niche" hardware still matter to system security. All it takes is a cheap programmable USB stick and a bit of knowledge.

For most users, the risk is small—unless someone can physically access your machine. But in shared workspaces, labs, or server rooms, this is a reminder: patch early, patch often, and beware strange USB devices!

References

- CVE-2022-3903 on Red Hat
- Kernel Patch Commit
- PyUSB
- GreatFET One


Feel free to share this with your sysadmin friends—safe USBing!

Timeline

Published on: 11/14/2022 21:15:00 UTC
Last modified on: 11/17/2022 20:23:00 UTC