CVE-2026-89738 (GCVE-0-2026-89738)
Vulnerability from cvelistv5
Published
2026-09-11 19:46
Modified
2026-10-21 12:48
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: usb: gadget: at91_udc: drain polled-VBUS timer/work before udc is freed In polled-VBUS mode (board.vbus_pin && board.vbus_polled), probe arms a self-restarting cycle: at91_vbus_timer() schedules vbus_timer_work, and at91_vbus_timer_work() calls at91_vbus_update() and re-arms the timer via mod_timer(). Both recover the same udc through container_of and dereference it on every iteration. Neither teardown path cancels this cycle. udc is devm-allocated, so it is freed after at91udc_remove() returns, and is likewise freed when probe fails and devres runs. A timer callback or work item that is pending or running at either point dereferences the freed udc. Add at91_udc_shutdown_vbus_timer() and call it from at91udc_remove() and from the usb_add_gadget_udc() failure path in probe; the remaining probe error paths fail before the timer is armed. timer_shutdown_sync() waits for a running callback and clears timer->function, which makes the work handler's mod_timer() a permanent no-op; cancel_work_sync() then drains any pending or running work whose re-arm attempt now does nothing. The timer must be shut down first, since cancelling the work alone would let the timer re-queue it. The guard mirrors probe: in IRQ mode the timer and work_struct are never initialized. This does not require a fault; a normal driver unbind can interleave with an already queued work item. This issue was found by an in-house static analysis tool.
References
Impacted products
Vendor Product Version
Linux Linux Version: 4037242c4f5ff77afe61bf07ca1e8a99490219e5
Version: 4037242c4f5ff77afe61bf07ca1e8a99490219e5
Version: 4037242c4f5ff77afe61bf07ca1e8a99490219e5
Version: 4037242c4f5ff77afe61bf07ca1e8a99490219e5
Version: 4037242c4f5ff77afe61bf07ca1e8a99490219e5
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{
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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/usb/gadget/udc/at91_udc.c"
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          "vendor": "Linux",
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        }
      ],
      "cpeApplicability": [
        {
          "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\nusb: gadget: at91_udc: drain polled-VBUS timer/work before udc is freed\n\nIn polled-VBUS mode (board.vbus_pin \u0026\u0026 board.vbus_polled), probe arms a\nself-restarting cycle: at91_vbus_timer() schedules vbus_timer_work, and\nat91_vbus_timer_work() calls at91_vbus_update() and re-arms the timer via\nmod_timer(). Both recover the same udc through container_of and dereference\nit on every iteration.\n\nNeither teardown path cancels this cycle. udc is devm-allocated, so it is\nfreed after at91udc_remove() returns, and is likewise freed when probe\nfails and devres runs. A timer callback or work item that is pending or\nrunning at either point dereferences the freed udc.\n\nAdd at91_udc_shutdown_vbus_timer() and call it from at91udc_remove() and\nfrom the usb_add_gadget_udc() failure path in probe; the remaining probe\nerror paths fail before the timer is armed. timer_shutdown_sync() waits\nfor a running callback and clears timer-\u003efunction, which makes the work\nhandler\u0027s mod_timer() a permanent no-op; cancel_work_sync() then drains\nany pending or running work whose re-arm attempt now does nothing. The\ntimer must be shut down first, since cancelling the work alone would let\nthe timer re-queue it. The guard mirrors probe: in IRQ mode the timer and\nwork_struct are never initialized.\n\nThis does not require a fault; a normal driver unbind can interleave with\nan already queued work item.\n\nThis issue was found by an in-house static analysis tool."
        }
      ],
      "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 use-after-free is reached on local AT91 UDC platform-driver teardown (sysfs unbind, rmmod, or probe-error unwind after the polled-VBUS timer is armed), not by parsing USB host packets. That matches other USB gadget/UDC teardown UAFs scored Local and is higher severity than Physical.\nAC:L - Once polled-VBUS mode is active, unbind or the usb_add_gadget_udc() failure path frees the devm-allocated udc while the self-restarting timer/work still hold it; the next timer tick or already-queued work then dereferences the freed object with no race the attacker cannot drive.\nPR:L - Highest reasonable exposure is a local account that manages the USB gadget/UDC on AT91 industrial, IoT, and embedded controllers, where platform unbind or gadget HAL access is often delegated beyond init-namespace root. Uncertain Low vs High, so Low per the overestimate rule.\nUI:N - The attacker initiates driver unbind, module unload, or a failing re-probe themselves; no separate victim action such as plugging a USB cable, mounting a filesystem, or opening a device node is required.\nS:U - The use-after-free corrupts the host kernel\u0027s struct at91_udc heap object within the same OS security authority and does not cross a VM, IOMMU, or sandbox boundary.\nC:H - at91_vbus_timer() and at91_vbus_timer_work() recover the freed udc via container_of and read vbus_pin, gadget state, and related fields; reclaiming that slab yields a classic UAF read/disclosure primitive.\nI:H - The dangling work calls at91_vbus_session()/pullup(), which write MMIO through udp_baseaddr and invoke caps-\u003epullup and possibly driver-\u003edisconnect on the freed object, enabling heap corruption and control-flow hijack.\nA:H - Dereferencing the freed udc from timer or workqueue context causes a kernel oops or panic even without a full exploit, so availability impact is High."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-21T12:48:31.419Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/723d73b245843d4fff4c3f42e857c78c2b2d414e"
        },
        {
          "url": "https://git.kernel.org/stable/c/a2a602cb1e28d76a5398cec3fa21b0110385f501"
        },
        {
          "url": "https://git.kernel.org/stable/c/51a311eb97e91ce1aed3005cb71ccb2e30f8cce8"
        },
        {
          "url": "https://git.kernel.org/stable/c/557ef547d49ff5e6026a4d39bdd3113bd81d7688"
        },
        {
          "url": "https://git.kernel.org/stable/c/c27d13ce4bab80fbdf6523928071b6c24b37606c"
        }
      ],
      "title": "usb: gadget: at91_udc: drain polled-VBUS timer/work before udc is freed",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89738",
    "datePublished": "2026-09-11T19:46:45.898Z",
    "dateReserved": "2026-09-11T19:38:34.761Z",
    "dateUpdated": "2026-10-21T12:48:31.419Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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