Vulnerability-Lookup

GHSA-WP68-7GHH-V4RV

Vulnerability from github – Published: 2026-08-15 06:32 – Updated: 2026-08-17 06:33

Details

In the Linux kernel, the following vulnerability has been resolved:

ALSA: seq: midi: Serialize output teardown with event_input

event_process_midi() borrows msynth->output_rfile.output and then passes the substream to dump_midi() and snd_rawmidi_kernel_write() without synchronizing with the output open/close transition. midisynth_use() also publishes output_rfile before snd_rawmidi_output_params() has finished.

The last midisynth_unuse() can therefore release the same rawmidi file and free substream->runtime before snd_rawmidi_kernel_write1() takes its runtime buffer reference. That leaves the event_input path using a stale substream or runtime and can end in a NULL-deref or use-after-free.

Fix this with two pieces of synchronization. Keep a short IRQ-safe spinlock only for publishing or clearing output_rfile and for pairing the output snapshot with an snd_use_lock_t reference. Once event_process_midi() has taken that in-flight reference, it drops the spinlock before calling snd_seq_dump_var_event(), dump_midi(), or snd_rawmidi_kernel_write(). midisynth_unuse() now detaches the visible rawmidi file under the same spinlock, waits for the in-flight writers to drain, and only then drains and releases the saved file. midisynth_use() likewise opens into a local snd_rawmidi_file and publishes it only after snd_rawmidi_output_params() succeeds.

The buggy scenario involves two paths, with each column showing the order within that path:

event_input path: last unuse path: 1. event_process_midi() snapshots 1. midisynth_unuse() starts output_rfile.output. tearing down output_rfile. 2. dump_midi() reaches 2. snd_rawmidi_kernel_release() snd_rawmidi_kernel_write() closes the output file. before runtime is pinned. 3. close_substream() frees 3. The callback keeps using substream->runtime. the borrowed substream.

Validation reproduced this kernel report: KASAN null-ptr-deref in snd_rawmidi_kernel_write1+0x56/0x360 RIP: 0033:0x7fde7dd0837f RIP: 0010:snd_rawmidi_kernel_write1+0x56/0x360

Severity

7.8 (High)


                  
                    CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

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{
  "affected": [],
  "aliases": [
    "CVE-2026-74387"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-15T06:22:40Z",
    "severity": "HIGH"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nALSA: seq: midi: Serialize output teardown with event_input\n\nevent_process_midi() borrows msynth-\u003eoutput_rfile.output and then\npasses the substream to dump_midi() and snd_rawmidi_kernel_write()\nwithout synchronizing with the output open/close transition.\nmidisynth_use() also publishes output_rfile before\nsnd_rawmidi_output_params() has finished.\n\nThe last midisynth_unuse() can therefore release the same rawmidi file\nand free substream-\u003eruntime before snd_rawmidi_kernel_write1() takes\nits runtime buffer reference. That leaves the event_input path using a\nstale substream or runtime and can end in a NULL-deref or use-after-free.\n\nFix this with two pieces of synchronization. Keep a short IRQ-safe\nspinlock only for publishing or clearing output_rfile and for pairing\nthe output snapshot with an snd_use_lock_t reference. Once\nevent_process_midi() has taken that in-flight reference, it drops the\nspinlock before calling snd_seq_dump_var_event(), dump_midi(), or\nsnd_rawmidi_kernel_write(). midisynth_unuse() now detaches the visible\nrawmidi file under the same spinlock, waits for the in-flight writers\nto drain, and only then drains and releases the saved file.\nmidisynth_use() likewise opens into a local snd_rawmidi_file and\npublishes it only after snd_rawmidi_output_params() succeeds.\n\nThe buggy scenario involves two paths, with each column showing the\norder within that path:\n\nevent_input path:                     last unuse path:\n1. event_process_midi() snapshots    1. midisynth_unuse() starts\n   output_rfile.output.                 tearing down output_rfile.\n2. dump_midi() reaches               2. snd_rawmidi_kernel_release()\n   snd_rawmidi_kernel_write()           closes the output file.\n   before runtime is pinned.         3. close_substream() frees\n3. The callback keeps using             substream-\u003eruntime.\n   the borrowed substream.\n\nValidation reproduced this kernel report:\nKASAN null-ptr-deref in snd_rawmidi_kernel_write1+0x56/0x360\nRIP: 0033:0x7fde7dd0837f\nRIP: 0010:snd_rawmidi_kernel_write1+0x56/0x360",
  "id": "GHSA-wp68-7ghh-v4rv",
  "modified": "2026-08-17T06:33:42Z",
  "published": "2026-08-15T06:32:32Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-74387"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/11165fe2c5ea0516debe486d91df67abbe36905e"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/718f6a56b40875f19e6915799044a02df9abfd52"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/936641af564c3d92721704b781e36aaf223efdd2"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/d6fd2afb137f52bf00c5210cc44d08ed54dcffb4"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ef7607ab1c8adc6258fb1b27d08e26aecdc18a58"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f5d470b808bc01f70978e22e595c6f7768313406"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}

CVE-2026-74387 (GCVE-0-2026-74387)

Vulnerability from cvelistv5 – Published: 2026-08-15 05:59 – Updated: 2026-08-17 05:46

Title

ALSA: seq: midi: Serialize output teardown with event_input

Summary

In the Linux kernel, the following vulnerability has been resolved: ALSA: seq: midi: Serialize output teardown with event_input event_process_midi() borrows msynth->output_rfile.output and then passes the substream to dump_midi() and snd_rawmidi_kernel_write() without synchronizing with the output open/close transition. midisynth_use() also publishes output_rfile before snd_rawmidi_output_params() has finished. The last midisynth_unuse() can therefore release the same rawmidi file and free substream->runtime before snd_rawmidi_kernel_write1() takes its runtime buffer reference. That leaves the event_input path using a stale substream or runtime and can end in a NULL-deref or use-after-free. Fix this with two pieces of synchronization. Keep a short IRQ-safe spinlock only for publishing or clearing output_rfile and for pairing the output snapshot with an snd_use_lock_t reference. Once event_process_midi() has taken that in-flight reference, it drops the spinlock before calling snd_seq_dump_var_event(), dump_midi(), or snd_rawmidi_kernel_write(). midisynth_unuse() now detaches the visible rawmidi file under the same spinlock, waits for the in-flight writers to drain, and only then drains and releases the saved file. midisynth_use() likewise opens into a local snd_rawmidi_file and publishes it only after snd_rawmidi_output_params() succeeds. The buggy scenario involves two paths, with each column showing the order within that path: event_input path: last unuse path: 1. event_process_midi() snapshots 1. midisynth_unuse() starts output_rfile.output. tearing down output_rfile. 2. dump_midi() reaches 2. snd_rawmidi_kernel_release() snd_rawmidi_kernel_write() closes the output file. before runtime is pinned. 3. close_substream() frees 3. The callback keeps using substream->runtime. the borrowed substream. Validation reproduced this kernel report: KASAN null-ptr-deref in snd_rawmidi_kernel_write1+0x56/0x360 RIP: 0033:0x7fde7dd0837f RIP: 0010:snd_rawmidi_kernel_write1+0x56/0x360

Severity

7.8 (High)


                        
                          CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Assigner

Linux mitre root

References

6 references

URL	Tags
https://git.kernel.org/stable/c/f5d470b808bc01f70…
https://git.kernel.org/stable/c/936641af564c3d927…
https://git.kernel.org/stable/c/718f6a56b40875f19…
https://git.kernel.org/stable/c/11165fe2c5ea0516d…
https://git.kernel.org/stable/c/d6fd2afb137f52bf0…
https://git.kernel.org/stable/c/ef7607ab1c8adc625…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < f5d470b808bc01f70978e22e595c6f7768313406 (git) Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 936641af564c3d92721704b781e36aaf223efdd2 (git) Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 718f6a56b40875f19e6915799044a02df9abfd52 (git) Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 11165fe2c5ea0516debe486d91df67abbe36905e (git) Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < d6fd2afb137f52bf00c5210cc44d08ed54dcffb4 (git) Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < ef7607ab1c8adc6258fb1b27d08e26aecdc18a58 (git)
Linux	Linux	Affected: 2.6.12 Unaffected: 0 , < 2.6.12 (semver) Unaffected: 6.1.178 , ≤ 6.1.* (semver) Unaffected: 6.6.145 , ≤ 6.6.* (semver) Unaffected: 6.12.97 , ≤ 6.12.* (semver) Unaffected: 6.18.40 , ≤ 6.18.* (semver) Unaffected: 7.1.5 , ≤ 7.1.* (semver) Unaffected: 7.2 , ≤ * (original_commit_for_fix)

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{
  "containers": {
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      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "sound/core/seq/seq_midi.c"
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              "version": "6.6.145",
              "versionType": "semver"
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              "status": "unaffected",
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              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.40",
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              "status": "unaffected",
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              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
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              "versionType": "original_commit_for_fix"
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        }
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nALSA: seq: midi: Serialize output teardown with event_input\n\nevent_process_midi() borrows msynth-\u003eoutput_rfile.output and then\npasses the substream to dump_midi() and snd_rawmidi_kernel_write()\nwithout synchronizing with the output open/close transition.\nmidisynth_use() also publishes output_rfile before\nsnd_rawmidi_output_params() has finished.\n\nThe last midisynth_unuse() can therefore release the same rawmidi file\nand free substream-\u003eruntime before snd_rawmidi_kernel_write1() takes\nits runtime buffer reference. That leaves the event_input path using a\nstale substream or runtime and can end in a NULL-deref or use-after-free.\n\nFix this with two pieces of synchronization. Keep a short IRQ-safe\nspinlock only for publishing or clearing output_rfile and for pairing\nthe output snapshot with an snd_use_lock_t reference. Once\nevent_process_midi() has taken that in-flight reference, it drops the\nspinlock before calling snd_seq_dump_var_event(), dump_midi(), or\nsnd_rawmidi_kernel_write(). midisynth_unuse() now detaches the visible\nrawmidi file under the same spinlock, waits for the in-flight writers\nto drain, and only then drains and releases the saved file.\nmidisynth_use() likewise opens into a local snd_rawmidi_file and\npublishes it only after snd_rawmidi_output_params() succeeds.\n\nThe buggy scenario involves two paths, with each column showing the\norder within that path:\n\nevent_input path:                     last unuse path:\n1. event_process_midi() snapshots    1. midisynth_unuse() starts\n   output_rfile.output.                 tearing down output_rfile.\n2. dump_midi() reaches               2. snd_rawmidi_kernel_release()\n   snd_rawmidi_kernel_write()           closes the output file.\n   before runtime is pinned.         3. close_substream() frees\n3. The callback keeps using             substream-\u003eruntime.\n   the borrowed substream.\n\nValidation reproduced this kernel report:\nKASAN null-ptr-deref in snd_rawmidi_kernel_write1+0x56/0x360\nRIP: 0033:0x7fde7dd0837f\nRIP: 0010:snd_rawmidi_kernel_write1+0x56/0x360"
        }
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      "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 - The bug is reached only via local ALSA sequencer interfaces: opening /dev/snd/seq, subscribing to a MIDI synth port (SNDRV_SEQ_IOCTL_SUBSCRIBE_PORT), writing events (snd_seq_write), and unsubscribing (SNDRV_SEQ_IOCTL_UNSUBSCRIBE_PORT). There is no network, Bluetooth, or physical-device packet path to event_process_midi().\nAC:L - Exploitation is a race between MIDI event delivery and the last midisynth_unuse() teardown; an attacker controls both sides by concurrently writing sequencer events and unsubscribing from the same MIDI output port. Published reproducers triggered KASAN null-deref/UAF reliably without external timing luck.\nPR:L - Any unprivileged local user with standard ALSA access (typically membership in the audio group for /dev/snd/seq) can create a sequencer client, subscribe to hardware MIDI synth ports, dispatch events, and trigger teardown. No real root/CAP_SYS_ADMIN or user-namespace capability is required.\nUI:N - Exploitation requires no victim interaction; the attacker programmatically opens the sequencer, subscribes, floods MIDI events, and unsubscribes from their own client. No mount, file open, or other user-driven action by another party is needed.\nS:U - Impact is kernel memory corruption and potential local privilege escalation within the same kernel security domain. It does not cross a VM/host, IOMMU, or sandbox boundary; compromised resources remain under the same OS authority.\nC:H - The race frees substream-\u003eruntime (kmalloc-192 snd_rawmidi_runtime) while event_process_midi() still dereferences it in dump_midi()/snd_rawmidi_kernel_write1(), producing a confirmed slab use-after-free and NULL-deref. UAF on kernel heap objects enables arbitrary memory disclosure via heap grooming.\nI:H - Use-after-free of the rawmidi runtime while the write path accesses runtime-\u003ebuffer and related fields can be turned into controlled heap corruption and arbitrary kernel writes/code execution, not merely a one-shot crash. Memory corruption primitives warrant High integrity impact.\nA:H - Concurrent unsubscribe frees the output runtime during an in-flight write, causing KASAN-reported null-pointer dereference and slab use-after-free in snd_rawmidi_kernel_write1(). This can oops or panic the kernel and be retriggered by repeated subscribe/write/unsubscribe cycles."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T05:46:36.550Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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        },
        {
          "url": "https://git.kernel.org/stable/c/11165fe2c5ea0516debe486d91df67abbe36905e"
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          "url": "https://git.kernel.org/stable/c/d6fd2afb137f52bf00c5210cc44d08ed54dcffb4"
        },
        {
          "url": "https://git.kernel.org/stable/c/ef7607ab1c8adc6258fb1b27d08e26aecdc18a58"
        }
      ],
      "title": "ALSA: seq: midi: Serialize output teardown with event_input",
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        "engine": "bippy-1.2.0"
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  "cveMetadata": {
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-74387",
    "datePublished": "2026-08-15T05:59:02.457Z",
    "dateReserved": "2026-08-15T05:44:03.890Z",
    "dateUpdated": "2026-08-17T05:46:36.550Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

Action not permitted

GHSA-WP68-7GHH-V4RV

CVE-2026-74387 (GCVE-0-2026-74387)

Tags

Sightings

Nomenclature