CVE-2026-64486: Linux Kernel Use-After-Free Vulnerability

CVE-2026-64486 Overview

CVE-2026-64486 is a NULL pointer dereference vulnerability in the Linux kernel's ALSA (Advanced Linux Sound Architecture) cmipci driver. The flaw resides in snd_cmipci_spdif_controls(), which invokes snd_ctl_new1() to allocate a new control element. When memory allocation fails, snd_ctl_new1() returns NULL, but the caller dereferences kctl->id.device without validating the return value. This leads to a kernel NULL pointer dereference, causing a kernel oops or panic during driver initialization on affected systems using C-Media CMI8x38 audio hardware.

Critical Impact
Successful triggering of the flaw results in a kernel NULL pointer dereference during ALSA sound card initialization, causing denial of service on affected Linux systems.

Affected Products

Linux kernel — ALSA cmipci sound driver (sound/pci/cmipci.c)
Systems using C-Media CMI8x38 PCI audio devices
Multiple stable kernel branches referenced in the upstream fix commits

Discovery Timeline

2026-07-25 - CVE-2026-64486 published to NVD
2026-07-25 - Last updated in NVD database

Technical Details for CVE-2026-64486

Vulnerability Analysis

The vulnerability is a NULL pointer dereference [CWE-476] in the ALSA cmipci driver used to support C-Media CMI8x38 PCI audio chipsets. The snd_cmipci_spdif_controls() function constructs S/PDIF control elements at driver probe time by calling snd_ctl_new1(). This helper allocates a struct snd_kcontrol from the provided template and can return NULL when memory allocation fails under pressure. The original code assumed the allocation always succeeded and immediately accessed the kctl->id.device member of the returned pointer without a NULL check.

When the allocation fails, dereferencing the returned NULL pointer produces an invalid memory access in kernel context. The fix adds NULL checks after each snd_ctl_new1() call and returns -ENOMEM when allocation fails, propagating the error cleanly up the initialization path.

Root Cause

The root cause is missing return-value validation from an allocation helper. snd_ctl_new1() is documented to return NULL on failure, but snd_cmipci_spdif_controls() did not check for this condition before dereferencing the returned pointer. This is a classic defensive-coding omission where the failure path of a kernel memory allocator was not handled.

Attack Vector

Triggering the flaw requires the cmipci driver to be loaded on a system with matching C-Media audio hardware, plus kernel memory allocation failure during control creation. Under normal conditions, exploitation requires local access and the ability to induce memory pressure. The impact is limited to a kernel crash or oops, denial of service rather than code execution or privilege escalation. There are no known public exploits and the CVE is not listed on CISA KEV.

No verified proof-of-concept code is available. See the upstream fix commits for the exact source-level change, including Kernel Git Commit 67e9ea9 and Kernel Git Commit b44888c.

Detection Methods for CVE-2026-64486

Indicators of Compromise

Kernel oops or panic messages referencing snd_cmipci_spdif_controls or snd_ctl_new1 in dmesg or /var/log/kern.log
ALSA sound card initialization failures on systems with C-Media CMI8x38 hardware
Unexpected loss of audio device availability after boot on affected kernels

Detection Strategies

Inventory Linux hosts and compare running kernel versions against the fixed versions referenced in the upstream stable commits
Audit hardware inventories for C-Media CMI8x38 audio adapters that load the cmipci module
Monitor kernel crash telemetry and core dumps for stack traces implicating the ALSA cmipci code path

Monitoring Recommendations

Forward kernel logs to a centralized log platform and alert on oops or panic events referencing snd_ctl_new1 or cmipci
Track kernel package versions across the fleet through configuration management to confirm patch deployment
Monitor system availability metrics on hosts with affected audio hardware to detect crash-induced downtime

How to Mitigate CVE-2026-64486

Immediate Actions Required

Apply the latest stable Linux kernel updates from your distribution vendor that include the upstream fix
Prioritize patching on systems that load the cmipci driver, particularly workstations with C-Media CMI8x38 audio hardware
If patching is not immediately possible, blacklist the cmipci module on systems where the audio device is not required

Patch Information

The fix adds NULL checks after each snd_ctl_new1() call in snd_cmipci_spdif_controls() and returns -ENOMEM when allocation fails. The patch is available in the mainline and multiple stable branches through the following commits: Kernel Git Commit 4dd5b0b, Kernel Git Commit 67e9ea9, Kernel Git Commit 8825a06, Kernel Git Commit af2b009, Kernel Git Commit b44888c, and Kernel Git Commit c205bd1.

Workarounds

Blacklist the cmipci kernel module on systems that do not require C-Media CMI8x38 audio support
Physically remove or disable the affected audio adapter in BIOS or UEFI where feasible
Restrict local access on multi-user systems to reduce the ability of unprivileged users to induce kernel memory pressure

bash

# Blacklist the cmipci driver until the kernel is patched
echo "blacklist snd_cmipci" | sudo tee /etc/modprobe.d/blacklist-cmipci.conf
sudo update-initramfs -u
sudo reboot