CVE-2026-53193

What it actually does

This is a Linux kernel use-after-free flaw in the ALSA timer subsystem. When an ALSA timer object is freed while timer instances are still associated with it, slave timer instances can retain pointers to freed kernel memory after the master timer instance is unlinked. Subsequent access to those stale timer references can dereference freed memory in kernel context. The most likely technical outcome is local denial of service through a kernel crash, but as with many kernel use-after-free conditions, privilege escalation may be possible if an attacker can reliably control memory reuse and trigger the stale access path.

Why it matters to the business

Successful exploitation could allow a local user or compromised low-privilege process to crash Linux systems that expose the affected ALSA timer functionality, disrupting workloads, user sessions, audio-dependent services, or desktop/edge systems. If exploit techniques mature, the risk could increase from system instability to full local privilege escalation. The current public exploitation signal is low: EPSS is 0.00141, there is no known CISA KEV listing, no ransomware association is reported, and no public exploit maturity is indicated. However, because this is kernel-level code, organizations should still patch through normal kernel maintenance cycles, prioritizing multi-user systems, developer workstations, desktops, kiosks, and systems where untrusted local users or sandbox escapes are realistic concerns.

How an attack unfolds

An attacker first needs local code execution or the ability to run a process that can interact with ALSA timer interfaces, such as the sound timer device. The attacker then creates userspace-driven ALSA timers and associated timer instances, including relationships where slave timer instances depend on a master timer instance. By coordinating timer creation, use, and close/free operations, the attacker attempts to force the kernel to free the underlying snd_timer object while related slave instances still reference it. After the stale pointer remains, the attacker triggers later operations against the affected timer path so the kernel dereferences memory that has already been freed. In a basic exploitation scenario this causes a kernel panic or crash. In a more advanced scenario, the attacker attempts to reclaim the freed memory with controlled data and convert the stale dereference into kernel memory corruption that could lead to privilege escalation.

How to fix it

Apply a Linux kernel update from the operating system or appliance vendor that includes the ALSA timer fix for this issue. The upstream fix changes timer cleanup behavior so pending timer instances are forcibly closed rather than merely unlinked, ensuring associated slave timer instances are properly detached before the timer object is released. No exact fixed package versions were provided in the input, so use vendor advisories for the relevant distribution, kernel stream, or appliance firmware to identify the corrected kernel build. After installing the updated kernel, reboot into the patched kernel and remove or de-prioritize boot entries for vulnerable kernels where operationally feasible. If immediate patching is not possible, reduce exposure by limiting local shell access, removing untrusted users, disabling or restricting access to sound devices where not required, disabling unnecessary ALSA timer/userspace timer functionality if supported by the platform, and applying mandatory access controls or container device restrictions to prevent untrusted workloads from accessing sound timer device nodes.

How to confirm the fix worked

Confirm the running kernel, not just the installed package, has been updated by checking the active kernel version after reboot and comparing it with the vendor advisory for this vulnerability. Verify that vulnerable older kernels are not still being booted by default. On systems built from source, confirm the ALSA timer patch is present by reviewing the kernel tree for changes that forcibly close pending snd_timer_instance objects during snd_timer_free() and guard repeated close operations with the dead-instance check. Where sound functionality is not required, validate that untrusted users and containers cannot access ALSA timer device nodes such as /dev/snd/timer. For exposure testing, inventory hosts with ALSA sound support enabled and check whether CONFIG_SND_TIMER and CONFIG_SND_UTIMER are present in the running kernel configuration. Avoid running untrusted proof-of-concept code on production systems because failed exploitation may crash the host.

Typical attack path

1. Obtain local execution on a Linux system with the affected ALSA timer subsystem available.
2. Open and interact with ALSA timer interfaces, commonly through the sound timer device.
3. Create userspace-driven timer objects and timer instances, including master/slave timer relationships.
4. Race or sequence timer close/free operations so the main timer object is released while dependent slave instances still reference it.
5. Trigger later timer activity or cleanup that dereferences the stale timer pointer.
6. Cause a kernel crash, or in a more advanced exploit, attempt controlled memory reuse to achieve kernel-level code execution or privilege escalation.

How to detect it

This vulnerability is most likely exploited locally, so detection should focus on endpoint and kernel telemetry rather than network indicators. Review kernel logs, system journals, crash dumps, and EDR telemetry for abnormal interaction with ALSA timer devices followed by kernel oops, panic, KASAN, or use-after-free messages. Important log sources include journalctl/kernel ring buffer logs, /var/log/kern.log, /var/log/messages, auditd events for device access, EDR process telemetry, and kernel crash dump systems such as kdump. Look for repeated or unusual opens of /dev/snd/timer by untrusted users or short-lived processes, followed by crashes referencing snd_timer_free(), snd_timer_close(), snd_timer_user, or ALSA timer cleanup. If KASAN or debug kernels are used, search specifically for use-after-free reports in ALSA timer code. There are no known public threat actors or ransomware campaigns tied to this issue, and no network-based indicators are expected.

• /dev/snd/timer
• CONFIG_SND_UTIMER
• CONFIG_SND_TIMER
• KASAN: use-after-free
• BUG: KASAN: use-after-free
• general protection fault
• kernel BUG
• kernel panic
• Oops:
• ALSA: timer
• snd_timer_free
• snd_timer_close
• snd_timer_close_locked
• snd_timer_instance
• snd_timer_user
• SNDRV_TIMER_IFLG_DEAD

What your security team should do

• Prioritize kernel updates for systems where untrusted local users, shared interactive access, desktop usage, developer workloads, kiosks, or containerized workloads with device access are present.
• Track vendor kernel advisories and map the fixed kernel build to each Linux distribution or appliance image in use, since no universal fixed version was provided.
• Ensure systems are rebooted into the patched kernel after package installation; kernel updates do not take effect until the new kernel is running.
• Restrict access to /dev/snd and especially /dev/snd/timer for users and containers that do not require sound timer functionality.
• Review container, sandbox, VDI, and desktop hardening policies to prevent unnecessary passthrough of host sound devices to untrusted workloads.
• Monitor kernel logs for ALSA timer crashes, KASAN use-after-free reports, kernel oopses, or panic events involving snd_timer functions.
• Treat unexpected kernel crashes involving ALSA timer paths as potentially security-relevant, preserving logs and crash dumps before reboot rotation removes evidence.
• Because EPSS is low and there is no KEV or known exploit maturity, handle this through risk-based kernel patching rather than emergency internet-edge remediation, unless local multi-user exposure is high.