CVE-2026-68202
Received Received - Intake

Use-After-Free in Linux Kernel ALSA Sequencer

Publication date: 2026-08-10

Last updated on: 2026-08-10

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: ALSA: seq: close a re-opened queue timer in the destructor queue_delete() closes the queue timer, then frees it. snd_seq_timer_close() clears q->timer->timeri. snd_use_lock_sync() then drains borrowers, and snd_seq_timer_delete() frees q->timer. A borrower can re-open the timer inside that window. A SET_QUEUE_CLIENT that took a queueptr() use_lock reference before the queue was unlinked runs snd_seq_timer_open() after the close. Open refuses re-open only while timeri is set, and the close just cleared it, so it re-opens timeri. snd_seq_timer_delete() does not close that instance. Its snd_seq_timer_stop() is a no-op, because running was cleared first. So it frees q->timer with the instance still live. The queue is freed next. The instance stays on the global timer with callback_data pointing at the freed queue. A non-owner START on the unlocked queue arms it. The next tick derefs the freed queue in snd_seq_timer_interrupt(). Reachable by an unprivileged user with access to /dev/snd/seq. No CAP and no queue ownership required. Close any lingering instance in the destructor. There, ->timeri can no longer change: the queue is unlinked and all use_lock borrowers have drained, so no snd_seq_queue_use() can re-open it. Close it before clearing q->timer. snd_timer_close() waits for any in-flight snd_seq_timer_interrupt() to finish, and that callback still reads q->timer (via snd_seq_check_queue()), so q->timer must stay valid until it drains.

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Meta Information

Published
2026-08-10
Last Modified
2026-08-10
Generated
2026-08-10
AI Q&A
2026-08-10
EPSS Evaluated
N/A
NVD
CVE-2026-68202
EUVD
EUVD-2026-55303

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *

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Exploitability

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This is a use-after-free vulnerability in the Linux kernel's ALSA sequencer subsystem. It occurs when a queue timer is closed and freed but later accessed through a stale pointer. An unprivileged user with access to /dev/snd/seq can trigger this by reopening a closed timer before it is fully destroyed, leading to a freed memory region being accessed by the timer interrupt handler.

Detection Guidance

This vulnerability is specific to the Linux kernel's ALSA sequencer subsystem and requires local access to /dev/snd/seq. Detection involves checking kernel logs for related errors or monitoring for unusual activity in the ALSA sequencer. No direct network detection commands are applicable.

Impact Analysis

This vulnerability could allow an attacker to cause a system crash or execute arbitrary code with kernel privileges. Since it is reachable by unprivileged users, it poses a significant security risk on affected Linux systems.

Mitigation Strategies

Update the Linux kernel to the latest stable version that includes the fix for this vulnerability. If immediate patching is not possible, restrict access to /dev/snd/seq by adjusting permissions or using mandatory access controls to limit exposure.

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