The vulnerability (CVE-2026-64479) in the Linux kernel ALSA subsystem's snd_seq_event_dup() function arises because the code conditionally clears a trailing word in a copied event cell based on the copied size compared to the event structure size. For legacy events, this condition is false, leaving the trailing word uninitialized and containing stale kernel heap data. Since the cell pool is allocated without zeroing and reused, this stale data can be leaked to user space when delivered to UMP-enabled clients that receive legacy events unconverted. This results in a 4-byte kernel heap information leak to unprivileged /dev/snd/seq clients. The fix involves comparing against the correct size and zeroing the trailing word for all shorter events to prevent leaking uninitialized memory.

An unprivileged local user with access to /dev/snd/seq can obtain a 4-byte kernel heap information leak, potentially disclosing sensitive kernel memory contents. This leak could aid attackers in further exploitation or bypassing security mechanisms. The impact is limited to information disclosure and does not directly allow privilege escalation or code execution.

A patch is available and should be applied by updating the Linux kernel to the fixed versions indicated by the vendor. After updating, a system reboot is required. The vendor advisory from Ubuntu (USN-8726-1) provides specific package versions that include the fix. No additional mitigation is required beyond applying the official kernel updates.