CVE-2026-64489: Linux Kernel Use-After-Free Vulnerability

CVE-2026-64489 Overview

CVE-2026-64489 is a NULL pointer dereference vulnerability in the Linux kernel's Advanced Linux Sound Architecture (ALSA) subsystem. The flaw exists in the snd_ymfpci_create_spdif_controls() function within the ymfpci sound driver. The function calls snd_ctl_new1() to allocate new control elements but fails to validate the return value before dereferencing kctl->id.device. When memory allocation fails, snd_ctl_new1() returns NULL, triggering a kernel NULL pointer dereference. The upstream patch adds NULL checks after each snd_ctl_new1() call and returns -ENOMEM when allocation fails.

Critical Impact
A local attacker triggering memory pressure during ymfpci driver initialization can cause a kernel NULL pointer dereference, leading to a denial-of-service condition on affected Linux systems.

Affected Products

Linux kernel versions containing the vulnerable snd_ymfpci_create_spdif_controls() implementation in the ALSA ymfpci driver
Systems using Yamaha YMF7xx PCI audio hardware with the affected kernel
Linux distributions shipping unpatched stable kernel branches referenced in the upstream commits

Discovery Timeline

2026-07-25 - CVE-2026-64489 published to the National Vulnerability Database
2026-07-25 - Last updated in NVD database

Technical Details for CVE-2026-64489

Vulnerability Analysis

The vulnerability resides in the ALSA ymfpci driver, which supports Yamaha YMF7xx family PCI sound cards. During driver initialization, snd_ymfpci_create_spdif_controls() creates S/PDIF-related control interfaces by calling the kernel helper snd_ctl_new1(). This helper allocates a new snd_kcontrol structure and can return NULL when kernel memory allocation fails under pressure. The original code dereferences the returned pointer immediately via kctl->id.device without validating it. The dereference of a NULL pointer within kernel context produces an oops, terminating the offending task and potentially destabilizing the system.

The patch introduces explicit NULL checks after every snd_ctl_new1() invocation and returns -ENOMEM when allocation fails, ensuring the driver initialization path fails gracefully.

Root Cause

The root cause is missing return-value validation on a memory allocation function. The snd_ctl_new1() API contract permits NULL returns under allocation failure, but the caller in snd_ymfpci_create_spdif_controls() assumed success. This pattern falls under NULL Pointer Dereference weaknesses, where trust in an allocator's success leads to unsafe field access.

Attack Vector

Exploitation requires the ymfpci driver to be loaded and reach the S/PDIF control creation path while the kernel slab allocator is unable to satisfy the request. A local attacker with the ability to induce memory pressure and trigger driver initialization (for example, via module reload on systems permitting it, or through hotplug events on hardware-equipped systems) can provoke the NULL dereference. The result is a kernel oops and denial of service. Because the code path executes in kernel context on driver setup, remote exploitation is not applicable without local hardware presence and privilege to influence module loading.

No public proof-of-concept exploit is available for CVE-2026-64489. See the referenced kernel Git commits for the exact source changes.

Detection Methods for CVE-2026-64489

Indicators of Compromise

Kernel oops or panic messages referencing snd_ymfpci_create_spdif_controls or snd_ctl_new1 in dmesg or /var/log/kern.log
Repeated failed loads of the snd_ymfpci kernel module coinciding with low-memory conditions
Sudden termination of audio subsystem initialization on systems with Yamaha YMF7xx hardware

Detection Strategies

Compare the running kernel version against the fixed commits listed in the upstream references to determine patch status
Audit kernel ring buffer output during boot and module load events for NULL pointer dereference traces in ALSA code paths
Monitor for abnormal -ENOMEM returns from ALSA control creation functions in kernel logs

Monitoring Recommendations

Forward kernel logs from Linux endpoints to a centralized log platform and alert on kernel oops signatures involving ALSA drivers
Track kernel package versions across the fleet using configuration management data to identify hosts running unpatched kernels
Correlate memory-pressure events with subsequent kernel faults to identify systems susceptible to allocation-failure bugs

How to Mitigate CVE-2026-64489

Immediate Actions Required

Update to a Linux kernel version that includes the fixes from the referenced upstream commits, including Kernel Git Commit 02f33c2 and Kernel Git Commit 18ec7d7
Apply distribution vendor kernel updates once they incorporate the ALSA ymfpci NULL-check patch
Inventory systems with Yamaha YMF7xx PCI audio hardware and prioritize their kernel upgrades

Patch Information

The fix is available in multiple stable kernel branches through the following upstream commits: Kernel Git Commit 02f33c2, Kernel Git Commit 18ec7d7, Kernel Git Commit 9109547, Kernel Git Commit d7c71df, Kernel Git Commit e64d170, and Kernel Git Commit f6538a3. Each commit adds NULL validation after snd_ctl_new1() calls and returns -ENOMEM on failure.

Workarounds

Blacklist the snd_ymfpci module on systems that do not require Yamaha YMF7xx audio support until a patched kernel is deployed
Restrict local user ability to load kernel modules by enforcing modules_disabled or kernel.modules_disabled=1 on hardened systems
Reduce exposure to memory-pressure conditions by tuning workload memory limits and cgroup constraints on multi-tenant hosts

bash

# Blacklist the vulnerable driver until patched kernel is installed
echo "blacklist snd_ymfpci" | sudo tee /etc/modprobe.d/blacklist-ymfpci.conf
sudo update-initramfs -u

# Verify current kernel version against fixed commits
uname -r