CVE-2026-74503 (GCVE-0-2026-74503)
Vulnerability from cvelistv5
Published
2026-08-15 12:27
Modified
2026-08-17 05:47
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: ALSA: timer: Clear SNDRV_TIMER_IFLG_DEAD once the close completes snd_timer_close_locked() marks an instance with SNDRV_TIMER_IFLG_DEAD and returns early when the flag is already set, but the flag is never cleared again. A completed close ends in remove_slave_links(), which leaves timeri->timer NULL, so a second close is already harmless through the timer == NULL path; the early return can only be reached by an instance that was opened again in between. For such an instance the close unlinks nothing, so snd_timer_instance_free() frees an object that is still on timer->open_list_head, still on snd_timer_master_list if it was opened with a slave key, still owns any adopted slaves, and still holds its timer and module references. snd_seq_timer_open() reopens an instance exactly like that: it retries its fallback open on the same object after a failure that has already run snd_timer_close_locked() internally. An unprivileged user with access to /dev/snd/timer and /dev/snd/seq can force that failure, since snd_timer_check_master() returns -EBUSY when a pending slave matches the new master's (slave_class, slave_id) key and the target timer has reached max_instances, and SNDRV_TIMER_IOCTL_SELECT with dev_class = SNDRV_TIMER_CLASS_SLAVE keeps the caller-supplied dev_sclass, so a sequencer queue's key can be forged. The freed instance is afterwards dereferenced by any further snd_timer_open() on that timer, by snd_timer_check_slave(), and by /proc/asound/timers, which faults on the stale ti->owner pointer. The flag only has to be visible while the close is in progress, which is all its other users need. Clear it in remove_slave_links(), under the same timer->lock that sets it, once the instance is off every list.
References
Impacted products
Vendor Product Version
Linux Linux Version: 586b219a22b1032b28b8bd356b963276c5e5bf53
Version: f46093dd22969037beb1fce2e043f3236be41c92
Version: da3039e91d1f835874ed6e9a33ea19ee80c2cb92
Version: da3039e91d1f835874ed6e9a33ea19ee80c2cb92
Version: 60e73ab87b84bbd6bd7ddd1d16019a3a3705ab8f
Version: 6.12.94   ≤
Version: 6.18.36   ≤
Version: 7.0.13   ≤
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
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          "programFiles": [
            "sound/core/timer.c"
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          "product": "Linux",
          "programFiles": [
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              "version": "7.1.8",
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              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
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      ],
      "cpeApplicability": [
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          "nodes": [
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              "cpeMatch": [
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nALSA: timer: Clear SNDRV_TIMER_IFLG_DEAD once the close completes\n\nsnd_timer_close_locked() marks an instance with SNDRV_TIMER_IFLG_DEAD\nand returns early when the flag is already set, but the flag is never\ncleared again.  A completed close ends in remove_slave_links(), which\nleaves timeri-\u003etimer NULL, so a second close is already harmless through\nthe timer == NULL path; the early return can only be reached by an\ninstance that was opened again in between.  For such an instance the\nclose unlinks nothing, so snd_timer_instance_free() frees an object that\nis still on timer-\u003eopen_list_head, still on snd_timer_master_list if it\nwas opened with a slave key, still owns any adopted slaves, and still\nholds its timer and module references.\n\nsnd_seq_timer_open() reopens an instance exactly like that: it retries\nits fallback open on the same object after a failure that has already\nrun snd_timer_close_locked() internally.  An unprivileged user with\naccess to /dev/snd/timer and /dev/snd/seq can force that failure, since\nsnd_timer_check_master() returns -EBUSY when a pending slave matches the\nnew master\u0027s (slave_class, slave_id) key and the target timer has\nreached max_instances, and SNDRV_TIMER_IOCTL_SELECT with dev_class =\nSNDRV_TIMER_CLASS_SLAVE keeps the caller-supplied dev_sclass, so a\nsequencer queue\u0027s key can be forged.  The freed instance is afterwards\ndereferenced by any further snd_timer_open() on that timer, by\nsnd_timer_check_slave(), and by /proc/asound/timers, which faults on the\nstale ti-\u003eowner pointer.\n\nThe flag only has to be visible while the close is in progress, which is\nall its other users need.  Clear it in remove_slave_links(), under the\nsame timer-\u003elock that sets it, once the instance is off every list."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - Exploitation requires local ioctl access to /dev/snd/timer and /dev/snd/seq to forge timer slave keys and drive snd_seq_timer_open() retry logic; there is no network, adjacent-wireless, or physical-device entry path.\nAC:L - The attacker fully controls the ioctl and sequencer queue sequence that forces the initial -EBUSY close, retries snd_timer_open() on the same instance, and later triggers free; no uncontrollable timing, memory layout, or rare kernel state is required beyond standard ALSA being enabled.\nPR:L - The fix commit and reachable ioctl paths require only an unprivileged local user with access to ALSA device nodes (/dev/snd/timer and /dev/snd/seq), typical on desktops, kiosks, and Android systems via the audio group or equivalent permissions, not real root in the init namespace.\nUI:N - Exploitation is self-contained through attacker-initiated timer SELECT ioctls and sequencer queue open/close operations; no victim interaction such as opening files, mounting filesystems, or clicking prompts is required.\nS:U - Impact is kernel memory corruption and potential local privilege escalation within the same kernel address space; it does not cross a VM, container, or IOMMU security boundary into a separate authority.\nC:H - A use-after-free of snd_timer_instance leaves dangling list pointers; freed memory can be reallocated and later dereferenced by snd_timer_open(), snd_timer_check_slave(), or /proc/asound/timers, enabling arbitrary kernel memory read primitives.\nI:H - The UAF frees a structure still linked on timer open/master lists while retaining timer and module references, allowing heap reuse and memory corruption that can be leveraged for arbitrary kernel writes or control-flow hijacking.\nA:H - Stale timer instance pointers are dereferenced during subsequent timer operations and /proc/asound/timers reads, causing kernel faults/oops; UAF reliably threatens crashes even before full exploitation."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T05:47:54.696Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/bb016091010ec401a06e6bdace0cd944ee03d371"
        },
        {
          "url": "https://git.kernel.org/stable/c/a26a2e52736f9e39843ca66a2e1ce6bf1adbcd1e"
        },
        {
          "url": "https://git.kernel.org/stable/c/0c561fab50991df10b1e4daca25886c34a2a9c07"
        },
        {
          "url": "https://git.kernel.org/stable/c/c2744d5f3aea474513fd2298daecb94a952ce441"
        }
      ],
      "title": "ALSA: timer: Clear SNDRV_TIMER_IFLG_DEAD once the close completes",
      "x_generator": {
        "engine": "bippy-1.2.0"
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  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-74503",
    "datePublished": "2026-08-15T12:27:28.208Z",
    "dateReserved": "2026-08-15T05:44:03.908Z",
    "dateUpdated": "2026-08-17T05:47:54.696Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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