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CVE-2026-89738 (GCVE-0-2026-89738)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:46 – Updated: 2026-09-13 06:33
VLAI
Title
usb: gadget: at91_udc: drain polled-VBUS timer/work before udc is freed
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.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 4037242c4f5ff77afe61bf07ca1e8a99490219e5 , < a2a602cb1e28d76a5398cec3fa21b0110385f501 (git)
Affected: 4037242c4f5ff77afe61bf07ca1e8a99490219e5 , < 51a311eb97e91ce1aed3005cb71ccb2e30f8cce8 (git)
Affected: 4037242c4f5ff77afe61bf07ca1e8a99490219e5 , < 557ef547d49ff5e6026a4d39bdd3113bd81d7688 (git)
Affected: 4037242c4f5ff77afe61bf07ca1e8a99490219e5 , < c27d13ce4bab80fbdf6523928071b6c24b37606c (git)
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Linux Linux Affected: 2.6.36
Unaffected: 0 , < 2.6.36 (semver)
Unaffected: 6.12.109 , ≤ 6.12.* (semver)
Unaffected: 6.18.50 , ≤ 6.18.* (semver)
Unaffected: 7.2.4 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc1 , ≤ * (original_commit_for_fix)
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/usb/gadget/udc/at91_udc.c"
          ],
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              "version": "0",
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              "versionType": "semver"
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              "status": "unaffected",
              "version": "6.18.50",
              "versionType": "semver"
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              "version": "7.2.4",
              "versionType": "semver"
            },
            {
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              "status": "unaffected",
              "version": "7.3-rc1",
              "versionType": "original_commit_for_fix"
            }
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        }
      ],
      "cpeApplicability": [
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          "nodes": [
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              "cpeMatch": [
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.109",
                  "versionStartIncluding": "2.6.36",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.50",
                  "versionStartIncluding": "2.6.36",
                  "vulnerable": true
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                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                  "vulnerable": true
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                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3-rc1",
                  "versionStartIncluding": "2.6.36",
                  "vulnerable": true
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              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "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."
        }
      ],
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        {
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            "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": [
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              "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": "2026-09-13T06:33:49.071Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
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          "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"
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      ],
      "title": "usb: gadget: at91_udc: drain polled-VBUS timer/work before udc is freed",
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  "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": "2026-09-13T06:33:49.071Z",
    "state": "PUBLISHED"
  },
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      "date": "2026-09-15",
      "epss": "0.00164",
      "percentile": "0.05937"
    },
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      "current_release_date": "2026-09-15T01:50:51.000Z",
      "cve": "CVE-2026-89738",
      "id": "msrc_CVE-2026-89738",
      "initial_release_date": "2026-09-13T01:09:23.000Z",
      "product_status:known_not_affected": "1",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "usb: gadget: at91_udc: drain polled-VBUS timer/work before udc is freed",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-89738.json",
      "version": "3"
    },
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    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-09-13T06:47:51+00:00",
      "cve": "CVE-2026-89738",
      "id": "CVE-2026-89738",
      "initial_release_date": "2026-09-11T19:46:45.898000+00:00",
      "product_status:known_affected": "2",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: Linux kernel: USB gadget `at91_udc` driver use-after-free vulnerability",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89738.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-09-15T23:59:30Z",
      "cve": "CVE-2026-89738",
      "id": "CVE-2026-89738",
      "initial_release_date": "2026-09-12T16:22:31Z",
      "product_status:known_affected": "324",
      "product_status:known_not_affected": "29",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-89738",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-89738.json",
      "version": "4"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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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.