GHSA-6695-37P4-X7M5
Vulnerability from github – Published: 2026-07-25 12:31 – Updated: 2026-07-25 12:31In the Linux kernel, the following vulnerability has been resolved:
ALSA: seq: Fix uninitialised heap leak in snd_seq_event_dup()
snd_seq_event_dup() copies an incoming event into a pool cell and, in the UMP-enabled build, clears the trailing cell->ump.raw.extra word that the memcpy() did not cover. The guard deciding whether to clear it compares the copied size against sizeof(cell->event):
memcpy(&cell->ump, event, size);
if (size < sizeof(cell->event))
cell->ump.raw.extra = 0;
For a legacy (non-UMP) event, size == sizeof(struct snd_seq_event) == sizeof(cell->event), so the condition is false and the extra word keeps stale data. The cell pool is allocated with kvmalloc() (not zeroed) and cells are reused via a free list, so that word holds uninitialised heap or leftover event data.
When such a cell is delivered to a UMP client (client->midi_version > 0) that set SNDRV_SEQ_FILTER_NO_CONVERT -- so the legacy event reaches it unconverted -- snd_seq_read() reads it out as the larger struct snd_seq_ump_event and copies the stale word to user space, a 4-byte kernel heap infoleak to an unprivileged /dev/snd/seq client.
Compare against sizeof(cell->ump) instead, so the trailing word is zeroed for every event shorter than the UMP cell.
{
"affected": [],
"aliases": [
"CVE-2026-64479"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-07-25T10:17:33Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nALSA: seq: Fix uninitialised heap leak in snd_seq_event_dup()\n\nsnd_seq_event_dup() copies an incoming event into a pool cell and, in\nthe UMP-enabled build, clears the trailing cell-\u003eump.raw.extra word that\nthe memcpy() did not cover. The guard deciding whether to clear it\ncompares the copied size against sizeof(cell-\u003eevent):\n\n\tmemcpy(\u0026cell-\u003eump, event, size);\n\tif (size \u003c sizeof(cell-\u003eevent))\n\t\tcell-\u003eump.raw.extra = 0;\n\nFor a legacy (non-UMP) event, size == sizeof(struct snd_seq_event) ==\nsizeof(cell-\u003eevent), so the condition is false and the extra word keeps\nstale data. The cell pool is allocated with kvmalloc() (not zeroed) and\ncells are reused via a free list, so that word holds uninitialised heap\nor leftover event data.\n\nWhen such a cell is delivered to a UMP client (client-\u003emidi_version \u003e 0)\nthat set SNDRV_SEQ_FILTER_NO_CONVERT -- so the legacy event reaches it\nunconverted -- snd_seq_read() reads it out as the larger struct\nsnd_seq_ump_event and copies the stale word to user space, a 4-byte\nkernel heap infoleak to an unprivileged /dev/snd/seq client.\n\nCompare against sizeof(cell-\u003eump) instead, so the trailing word is zeroed\nfor every event shorter than the UMP cell.",
"id": "GHSA-6695-37p4-x7m5",
"modified": "2026-07-25T12:31:37Z",
"published": "2026-07-25T12:31:37Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-64479"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/435990e25bf1f4af3e6df12a6fbfd1f7ba4a97d4"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/651ba82fe2a144bc7356d940bfd235c3810b0549"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/6ded42615fa1f4949925afd0a8a9e1ab3bf96202"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/a224c84e5d3d35708c082c84ad12d81d90762195"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/d7649aa11089a93ea2285c210397aa67e5800766"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/ea672a9f6cc38f06fe69dd2c257ef8a3d4db179a"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/fb1aa5082847b98f44f9c6272aee9d0dca9244f0"
}
],
"schema_version": "1.4.0",
"severity": []
}
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