{"id":"CVE-2026-68200","title":"ALSA: timer: don't re-enter an instance callback that is still running","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nALSA: timer: don't re-enter an instance callback that is still running\n\nThe userspace-driven timer (utimer) TRIGGER ioctl calls\nsnd_timer_interrupt() directly with no s…","severity":"high","cvss":7.8,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","cvssSource":"cna","vendor":"Linux","product":"Linux","affected":["Linux >= 37745918e0e7575bc40f38da93a99b9fa6406224 < 996c24377eea4d4506b7c3ccbbf1e490440b5e0b","Linux >= 37745918e0e7575bc40f38da93a99b9fa6406224 < 1395327a96614885552bae5fbb650e6dd182d49b","Linux >= 37745918e0e7575bc40f38da93a99b9fa6406224 < c1078130a4cd7e738f4b73afe99b3e68cbfbf884","Linux >= 37745918e0e7575bc40f38da93a99b9fa6406224 < 70d28bfcd6224eed75986b3b987b997e59643fa4","Linux 6.12"],"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"total","timestamp":"2026-10-16T15:45:45.952890Z"},"published":"2026-08-10","updated":"2026-10-16","sourceUpdated":"2026-10-16T15:53:03.285Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-68200","references":[{"url":"https://git.kernel.org/stable/c/996c24377eea4d4506b7c3ccbbf1e490440b5e0b"},{"url":"https://git.kernel.org/stable/c/1395327a96614885552bae5fbb650e6dd182d49b"},{"url":"https://git.kernel.org/stable/c/c1078130a4cd7e738f4b73afe99b3e68cbfbf884"},{"url":"https://git.kernel.org/stable/c/70d28bfcd6224eed75986b3b987b997e59643fa4"}],"tags":["cve.org"],"epss":0.0017,"epssPercentile":0.05976,"ingestedAt":"2026-10-16T17:24:46.849Z","slug":"CVE-2026-68200","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nALSA: timer: don't re-enter an instance callback that is still running\n\nThe userspace-driven timer (utimer) TRIGGER ioctl calls\nsnd_timer_interrupt() directly with no serialization, so two threads\ntriggering the same utimer can run snd_timer_interrupt() on one\nsnd_timer concurrently.\n\nsnd_timer_process_callbacks() drops timer->lock around each instance\ncallback and marks the in-flight callback with the single\nSNDRV_TIMER_IFLG_CALLBACK bit; snd_timer_close_locked() waits on that\nbit to drain an in-flight callback before freeing the instance. The bit\ncannot represent two concurrent callbacks: when a second interrupt\nre-queues an instance whose callback is still running, both run at once,\nthe first to finish clears the bit, and the close-path drain then frees\nthe instance (and its callback_data) while the other callback is still\nlive - a use-after-free reachable by any user able to open\n/dev/snd/timer, both via a user timer instance and via a sequencer queue\ntimer bound to the utimer.\n\nsnd_timer_interrupt() sets IFLG_CALLBACK before dropping timer->lock, so\na concurrent interrupt already observes it under the lock. Skip\nre-queuing an instance (and its slaves) to the ack/sack list while its\ncallback is in flight; the accumulated pticks are delivered on the next\ntick, so no event is lost.\n\n## Affected\n\n- `Linux >= 37745918e0e7575bc40f38da93a99b9fa6406224 < 996c24377eea4d4506b7c3ccbbf1e490440b5e0b`\n- `Linux >= 37745918e0e7575bc40f38da93a99b9fa6406224 < 1395327a96614885552bae5fbb650e6dd182d49b`\n- `Linux >= 37745918e0e7575bc40f38da93a99b9fa6406224 < c1078130a4cd7e738f4b73afe99b3e68cbfbf884`\n- `Linux >= 37745918e0e7575bc40f38da93a99b9fa6406224 < 70d28bfcd6224eed75986b3b987b997e59643fa4`\n- `Linux 6.12`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":43,"depthScoreParts":{"impact":42.9,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}