CVE-2026-68202
HighCVSS 7.8Exploitation Probability (EPSS)
Low risk7th percentile - higher than 7% of all known CVEs
Summary
A vulnerability was found in the Linux kernel's ALSA sequencer subsystem. The issue is that the queue deletion function does not close a re-opened timer, leading to a use-after-free condition. An attacker with access to /dev/snd/seq can exploit this flaw to corrupt kernel memory.
Risk Assessment
The vulnerability allows an unprivileged user (without CAP_SYS_ADMIN and without queue ownership) to trigger a kernel memory safety violation, potentially leading to privilege escalation or system crash (DoS).
Recommendation
Immediately apply the official Linux kernel patch that closes lingering timer instances in the queue destructor. Also restrict access to /dev/snd/seq for unprivileged users if feasible.
Original NVD description (English source)
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.