CVE-2026-53192: Linux Kernel ALSA Timer Use-After-Free Privilege Escalation

Technical summary

The vulnerability is a use-after-free (UAF) condition in the ALSA timer code, specifically in the snd_timer_user_params() function. When snd_timer_free() is invoked during timer object release (e.g., userspace timer closure), it detaches and frees timer instances. However, concurrent ioctl calls—particularly SNDRV_TIMER_IOCTL_PARAMS—can race with this cleanup because the ioctl handler lacks the register_mutex protection that guards most other timer-related ioctl operations. This allows a thread to dereference a timer instance pointer after the underlying timer object has been freed. The patch adds register_mutex locking around snd_timer_user_params() to serialize access and prevent the race.

Business impact

Systems running vulnerable Linux kernels with CONFIG_SND_UTIMER enabled are exposed to local privilege escalation and denial-of-service attacks. An unprivileged local user can exploit the race condition to achieve code execution in the kernel context or trigger a kernel crash, disrupting audio services and potentially affecting dependent applications. The impact is limited to systems where the attacker already has local user access, but the ability to escalate privileges or crash the kernel makes this a significant operational and security concern for multi-user systems and containerized environments.

Affected systems

All versions of the Linux kernel with the ALSA timer subsystem (CONFIG_SND_UTIMER) are affected. The vulnerability applies across all supported Linux distributions shipping vulnerable kernel versions. Specific affected kernel versions and patch availability depend on the distribution's kernel branch; consult your vendor's security advisory for exact version information. Systems that do not have CONFIG_SND_UTIMER enabled or do not expose audio timer functionality to unprivileged users have reduced risk.

Exploitability

Exploitability is HIGH. The vulnerability requires only local user-level access and no special privileges—any authenticated local user can attempt exploitation. The race condition is relatively straightforward to trigger through concurrent ioctl calls from multiple threads or processes. No user interaction is required. However, the race is timing-dependent, so reliable exploitation may require some trial or tuning. Public exploits and proof-of-concept code have not been confirmed; however, the simplicity of the vulnerability suggests proof-of-concept development is feasible.

Remediation

Apply a kernel patch that adds register_mutex protection to the SNDRV_TIMER_IOCTL_PARAMS handler in the ALSA timer code. Most distributions will backport this fix to their supported kernel branches. Alternatively, disabling CONFIG_SND_UTIMER at compile time eliminates the vulnerability but may break applications relying on userspace timer functionality. As a temporary mitigation, restrict ioctl access to the ALSA timer devices via file permissions or SELinux policy, though this is not a complete fix.

Patch guidance

Check your Linux distribution's security advisory for the patched kernel version addressing CVE-2026-53192. The fix involves a targeted mutex addition to snd_timer_user_params() and is a low-risk change. Update your kernel to the patched version via your distribution's standard package manager (e.g., apt, yum, dnf). After patching, reboot systems to load the fixed kernel. Verify that the patch has been applied by checking the kernel version and confirming the ALSA timer code includes the register_mutex protection.

Detection guidance

Monitor system logs and kernel warnings for UAF-related crashes in the ALSA timer subsystem (look for 'KASAN' or 'use-after-free' messages involving snd_timer). Intrusion detection systems should flag unusual concurrent access to /dev/snd/timer* devices by the same user from multiple processes. Watch for unexpected kernel oops or panics involving the timer module. Runtime tools like AddressSanitizer (KASAN) can help detect the UAF at runtime if enabled in the kernel build. Post-patch verification can include fuzzing the SNDRV_TIMER_IOCTL_PARAMS ioctl with concurrent calls to confirm the race is eliminated.

Why prioritize this

This vulnerability scores HIGH (CVSS 7.8) due to its local exploitability, lack of privilege requirements, and direct impact on system integrity and confidentiality. The race condition is reliable to trigger and grants full kernel-context code execution or denial-of-service capabilities to any local user. Rapid patching is warranted for any system exposing local user access, particularly shared hosting, multi-user systems, and container environments where user isolation is critical.

Risk score, explained

The CVSS 3.1 score of 7.8 (HIGH severity) reflects: Attack Vector = Local (AV:L) because exploitation requires local system access; Attack Complexity = Low (AC:L) because the race is straightforward to trigger; Privileges Required = Low (PR:L) because any local user can exploit it; User Interaction = None (UI:N) because no user action is needed; and the impact spans Confidentiality, Integrity, and Availability (C:H, I:H, A:H) due to kernel code execution and crash potential. The lack of CVSS temporal factors (no active KEV listing) does not diminish urgency for systems with local user populations.

Frequently asked questions