CVE-2024-53239

What it actually does

Use-after-free in the ALSA 6fire USB audio driver caused by calling usb6fire_chip_destroy() at USB disconnect while the sound card object may still be referenced via snd_card_free_when_closed(); resources are now released in the card's private_free callback instead.

Why it matters to the business

Kernel memory corruption or crashes on systems using the 6fire USB audio device, potentially leading to denial of service or local privilege escalation; older Ubuntu LTS kernels are affected but the flaw is narrowly scoped to one driver.

How an attack unfolds

An attacker with local access triggers repeated USB connect/disconnect cycles for a 6fire device while user-space audio applications hold references to the card; the timing window allows the freed object to be dereferenced, resulting in a use-after-free that can be leveraged for arbitrary code execution.

How to fix it

Upgrade to a fixed kernel package for each affected Ubuntu release: linux 3.13.0-133.182 (14.04), 4.4.0-57.78 (16.04), linux-aws 4.4.0-1002.2 / 4.4.0-1001.10, linux-azure 4.15.0-1023.24~14.04.1 / 4.11.0-1009.9, linux-lts-xenial 4.4.0-57.78~14.04.1, linux-hwe 4.8.0-36.36~16.04.1 and the corresponding fixed versions for euclid, gcp, gke, kvm, oem, raspi2 and snapdragon packages.

How to confirm the fix worked

Verify the running kernel version matches or exceeds one of the listed fixed packages; confirm the 6fire driver source contains the private_free resource release logic; test by attaching a 6fire device and exercising snd_card_free_when_closed() under load.

Typical attack path

1. Obtain local shell on target system with a 6fire USB audio device attached
2. Trigger snd_card_free_when_closed() path while simultaneously forcing USB disconnect
3. Race the manual usb6fire_chip_destroy() call against card object lifetime
4. Reuse the dangling pointer via crafted audio operations or memory spraying
5. Escalate to kernel code execution or trigger denial of service

How to detect it

Search kernel logs and dmesg for 6fire driver messages around USB disconnect events, look for use-after-free warnings or slab corruption reports referencing usb6fire_chip_abort or snd_card_free_when_closed, and correlate with unexpected audio subsystem crashes.

What your security team should do

• Patch all listed Ubuntu kernel packages to the exact fixed versions provided
• Remove or disable 6fire USB audio devices on systems that cannot be immediately updated
• Monitor kernel logs for 6fire-related oops or UAF warnings until patching is complete
• Restrict local USB device access via udev or AppArmor profiles where feasible