CVE-2018-19824

What it actually does

Use-after-free in the ALSA USB audio driver (usb_audio_probe in sound/usb/card.c) triggered when a malicious USB sound device with zero interfaces is connected, allowing local code execution or kernel crash.

Why it matters to the business

Local attackers with USB access can fully compromise affected Linux systems, leading to data theft, persistence, or denial of service; high downstream prevalence in the Linux ecosystem increases exposure across servers and endpoints.

How an attack unfolds

An attacker crafts a USB sound device that reports zero interfaces and connects it to a vulnerable Linux system; the kernel's ALSA probe mishandles the device, triggering the use-after-free that the attacker leverages for arbitrary code execution.

How to fix it

Upgrade the Linux kernel to a version containing commit 5f8cf712582617d523120df67d392059eaf2fc4b or later; apply vendor-supplied kernel updates for all affected distributions.

How to confirm the fix worked

Verify the running kernel contains commit 5f8cf712582617d523120df67d392059eaf2fc4b or a backport; test by connecting non-malicious USB audio devices and confirming no kernel oops or panic occurs.

Typical attack path

1. Prepare a malicious USB sound device that advertises zero interfaces
2. Physically connect the device to the target Linux system
3. Kernel invokes usb_audio_probe during device enumeration
4. Trigger use-after-free condition in ALSA driver
5. Leverage freed object for code execution or system crash

How to detect it

Review kernel logs (dmesg, /var/log/kern.log) for USB audio probe failures or use-after-free warnings around device connection events; correlate with physical security logs showing unexpected USB insertions.

What your security team should do

• Immediately apply the referenced kernel commit or latest distribution kernel package
• Restrict physical USB access on high-value systems until patched
• Monitor kernel logs for USB audio probe errors on unpatched hosts
• Prioritize patching on systems with high EPSS exposure or external USB ports