CVE-2026-53193: Linux Kernel ALSA Timer Use-After-Free Vulnerability

Technical summary

CVE-2026-53193 is a use-after-free vulnerability (CWE-416) in the Linux kernel's sound timer infrastructure. The issue arises during snd_timer_free() when pending snd_timer_instance objects remain linked to the timer object. Previously, the kernel would simply unlink instances and set their timer pointers to NULL, then immediately release resources. However, when slave timer instances are associated with a master instance that is linked to the timer being freed, those slave instances retain dangling pointers to the freed timer object. The vulnerability is particularly exploitable with userspace-driven timers (CONFIG_SND_UTIMER) that allow creation and deletion via file operations. The fix modifies the cleanup path to invoke snd_timer_close[_locked]() for each pending instance, ensuring proper detachment of all associated slave instances before resource deallocation, and adds a SNDRV_TIMER_IFLG_DEAD check to prevent double-closure.

Business impact

A local attacker with unprivileged user access can exploit this vulnerability to cause kernel memory corruption or denial of service. By manipulating timer object lifecycle—particularly through userspace timer creation and deletion—an attacker can trigger use-after-free conditions that may lead to system crashes, information disclosure, or potentially code execution. Audio and multimedia applications, as well as any system relying on ALSA timers for scheduling, could be affected. The HIGH CVSS score (7.8) reflects the severity: local access requirement, but with high impact on confidentiality, integrity, and availability.

Affected systems

The vulnerability affects Linux kernel systems with ALSA (Advanced Linux Sound Architecture) timer functionality enabled. It is most readily triggered on systems with CONFIG_SND_UTIMER enabled, which allows userspace applications to create and manage timer objects directly. Any Linux distribution shipping a kernel version prior to the fix is potentially vulnerable. This includes desktop, server, and embedded systems that use ALSA for audio and timing services.

Exploitability

Exploitability is moderate but practical for local attackers. The vulnerability requires local code execution on the target system (unprivileged user context is sufficient based on the CVSS vector), but no user interaction is needed. The exploit path is relatively straightforward: an attacker must create a scenario where a userspace timer is created, linked to slave instances, and then destroyed while other code attempts to access those instances. CONFIG_SND_UTIMER significantly lowers the bar, as it exposes timer creation to userspace directly. The vulnerability is not currently tracked in the CISA KEV catalog, indicating it has not yet been exploited in confirmed active attacks, but this does not diminish its technical merit or the importance of rapid patching.

Remediation

The Linux kernel fix resolves the issue by modifying the timer cleanup path to forcibly close all pending timer instances via snd_timer_close[_locked]() rather than simply unlinking them. This ensures that master-slave relationships are properly unwound and all dangling references are cleared before memory is freed. Additionally, a SNDRV_TIMER_IFLG_DEAD flag check is added to guard against double-closure. System administrators should apply the available kernel security update as soon as feasible. Verify the patch version against your distribution's advisory.

Patch guidance

Apply the kernel security update provided by your Linux distribution. Patches will be available through standard update channels (e.g., apt, yum, zypper depending on distribution). Verify that the kernel update includes the fix for snd_timer_free() described in CVE-2026-53193. Systems with CONFIG_SND_UTIMER enabled should prioritize patching due to increased attack surface. Reboot may be required to apply the update. Organizations should test patches in a pre-production environment if feasible before broad rollout.

Detection guidance

Monitor system logs for repeated ALSA timer errors, audio subsystem crashes, or kernel panics that correlate with userspace timer activity. Systems with CONFIG_SND_UTIMER enabled should be monitored for unusual timer creation and destruction patterns. Kernel address sanitizer (KASAN) or other memory safety tools may detect use-after-free conditions if enabled in a test environment. EDR and kernel-level monitoring tools can flag access to freed memory regions associated with timer structures. Post-exploitation, evidence may appear as audio subsystem instability, denial of service, or unexplained kernel crashes.

Why prioritize this

This vulnerability merits high priority due to its HIGH CVSS score (7.8), local attack vector with unprivileged access requirement, and high impact across all CIA triad dimensions. Although not yet in the CISA KEV, the practical exploitability—especially on systems with CONFIG_SND_UTIMER—and the straightforward attack path (file operations triggering cleanup logic) make it a credible near-term threat. Organizations with audio-capable systems or embedded devices using ALSA should patch urgently.

Risk score, explained

The CVSS 3.1 score of 7.8 (HIGH) reflects: local attack vector (AV:L), low attack complexity (AC:L), low privilege requirement (PR:L), no user interaction (UI:N), unchanged scope (S:U), and high impact to confidentiality, integrity, and availability (C:H/I:H/A:H). The score appropriately captures the severity of a use-after-free in kernel timer infrastructure accessible to local users, where successful exploitation can corrupt kernel memory or crash the system.

Frequently asked questions