GHSA-FP39-RJ9V-7XC4
Vulnerability from github – Published: 2026-10-18 18:32 – Updated: 2026-10-30 15:34In the Linux kernel, the following vulnerability has been resolved:
USB: cdc-acm: skip URB restart in port_shutdown if disconnected
acm_port_shutdown() is called from the tty-port machinery whenever the last user closes the port. acm_disconnect() sets acm->disconnected and calls tty_port_tty_vhangup(), which eventually triggers port_shutdown(). At that point acm_disconnect() has already called acm_poison_urbs() and is about to free the control and read URBs.
However, acm_port_shutdown() unconditionally calls acm_unpoison_urbs() and, when the ALWAYS_POLL_CTRL quirk is set, immediately re-submits the ctrlurb and all read URBs. If the concurrent acm_disconnect() then frees those URBs and their DMA buffers while they are in-flight, the result is a use-after-free in acm_ctrl_irq() or acm_read_bulk_callback() accessing the freed DMA memory.
Fix by checking acm->disconnected after draining the delayed anchor and returning early: if we are in a disconnect path the URBs must remain poisoned and must not be resubmitted.
The early return is placed after the delayed-anchor drain loop because that loop only cancels write-side accounting (wb->use = false and autopm counter) and does not touch the hardware path.
{
"affected": [],
"aliases": [
"CVE-2026-98773"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-10-18T16:17:31Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nUSB: cdc-acm: skip URB restart in port_shutdown if disconnected\n\nacm_port_shutdown() is called from the tty-port machinery whenever the\nlast user closes the port. acm_disconnect() sets acm-\u003edisconnected and\ncalls tty_port_tty_vhangup(), which eventually triggers port_shutdown().\nAt that point acm_disconnect() has already called acm_poison_urbs() and\nis about to free the control and read URBs.\n\nHowever, acm_port_shutdown() unconditionally calls acm_unpoison_urbs()\nand, when the ALWAYS_POLL_CTRL quirk is set, immediately re-submits the\nctrlurb and all read URBs. If the concurrent acm_disconnect() then\nfrees those URBs and their DMA buffers while they are in-flight, the\nresult is a use-after-free in acm_ctrl_irq() or acm_read_bulk_callback()\naccessing the freed DMA memory.\n\nFix by checking acm-\u003edisconnected after draining the delayed anchor and\nreturning early: if we are in a disconnect path the URBs must remain\npoisoned and must not be resubmitted.\n\nThe early return is placed after the delayed-anchor drain loop because\nthat loop only cancels write-side accounting (wb-\u003euse = false and\nautopm counter) and does not touch the hardware path.",
"id": "GHSA-fp39-rj9v-7xc4",
"modified": "2026-10-30T15:34:00Z",
"published": "2026-10-18T18:32:02Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98773"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/420ca35af891d33522cc08504768ccd60a4c450a"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/9742905d9ed5bf23ebe4c100dec80b6bc50fb522"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/a0ed07b5bbb2d8fcef86810453216070691816e7"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/d86775e79838d7d2e38ccf506a7d0f8e2dd4d5d0"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/d97da42e9de577dc827d4e8866e6971deefe2d9c"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/dc614d6bc991740d41d5a99ac7765c4b675dda88"
}
],
"schema_version": "1.4.0",
"severity": []
}
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