CVE-2026-89894 (GCVE-0-2026-89894)
Vulnerability from cvelistv5
Published
2026-09-16 10:31
Modified
2026-10-19 08:54
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: media: cx231xx: reject geometry changes while the VBI queue is busy vidioc_s_fmt_vid_cap() and vidioc_s_std() change the device-wide dev->width / dev->norm but only refuse the change when the *video* queue (dev->vidq) is busy. The VBI queue (dev->vbiq) shares that same geometry: cx231xx_init_vbi_isoc() latches dma_q->lines_per_field from dev->norm, the VBI videobuf2 plane is sized from dev->width / dev->norm in vbi_queue_setup() and vbi_buf_prepare(), and cx231xx_do_vbi_copy() then recomputes the destination offset from the *live* dev->width and the latched lines_per_field on every URB completion: offset = lines_completed * (dev->width << 1) + ...; if (dma_q->current_field == 2) offset += dev->width * 2 * dma_q->lines_per_field; memcpy(plane + offset, p_buffer, lencopy); Because the VBI node shares video_ioctl_ops with the video node, an application can size a small VBI plane (REQBUFS/QBUF with a small width, or with the NTSC standard), then enlarge dev->width (or switch dev->norm to PAL) through the video node while the VBI stream is running -- the change is allowed because only dev->vidq is checked -- and let the device deliver a field-2 VBI payload. cx231xx_do_vbi_copy() now computes the offset with the larger geometry and memcpy()s past the end of the smaller plane that was already allocated, a heap out-of-bounds write whose offset is attacker-chosen and whose contents come from the device. The per-field guard in cx231xx_copy_vbi_line() does not help: it bounds the copy against the latched lines_per_field, not the plane's real capacity, and vb2 does not re-run buf_prepare() for an already prepared buffer. Refuse the format/standard change when the VBI queue is busy as well, so the geometry cannot change underneath an allocated VBI buffer.
References
Impacted products
Vendor Product Version
Linux Linux Version: 7c617138b8254a6bb60bfb5b8fc53eb8b3d6c3ab
Version: 7c617138b8254a6bb60bfb5b8fc53eb8b3d6c3ab
Version: 7c617138b8254a6bb60bfb5b8fc53eb8b3d6c3ab
Version: 7c617138b8254a6bb60bfb5b8fc53eb8b3d6c3ab
Version: 7c617138b8254a6bb60bfb5b8fc53eb8b3d6c3ab
Version: 7c617138b8254a6bb60bfb5b8fc53eb8b3d6c3ab
Version: 7c617138b8254a6bb60bfb5b8fc53eb8b3d6c3ab
Version: 7c617138b8254a6bb60bfb5b8fc53eb8b3d6c3ab
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{
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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/media/usb/cx231xx/cx231xx-video.c"
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              ],
              "negate": false,
              "operator": "OR"
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          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmedia: cx231xx: reject geometry changes while the VBI queue is busy\n\nvidioc_s_fmt_vid_cap() and vidioc_s_std() change the device-wide\ndev-\u003ewidth / dev-\u003enorm but only refuse the change when the *video* queue\n(dev-\u003evidq) is busy. The VBI queue (dev-\u003evbiq) shares that same geometry:\ncx231xx_init_vbi_isoc() latches dma_q-\u003elines_per_field from dev-\u003enorm,\nthe VBI videobuf2 plane is sized from dev-\u003ewidth / dev-\u003enorm in\nvbi_queue_setup() and vbi_buf_prepare(), and cx231xx_do_vbi_copy() then\nrecomputes the destination offset from the *live* dev-\u003ewidth and the\nlatched lines_per_field on every URB completion:\n\n\toffset = lines_completed * (dev-\u003ewidth \u003c\u003c 1) + ...;\n\tif (dma_q-\u003ecurrent_field == 2)\n\t\toffset += dev-\u003ewidth * 2 * dma_q-\u003elines_per_field;\n\tmemcpy(plane + offset, p_buffer, lencopy);\n\nBecause the VBI node shares video_ioctl_ops with the video node, an\napplication can size a small VBI plane (REQBUFS/QBUF with a small width,\nor with the NTSC standard), then enlarge dev-\u003ewidth (or switch dev-\u003enorm\nto PAL) through the video node while the VBI stream is running -- the\nchange is allowed because only dev-\u003evidq is checked -- and let the device\ndeliver a field-2 VBI payload. cx231xx_do_vbi_copy() now computes the\noffset with the larger geometry and memcpy()s past the end of the smaller\nplane that was already allocated, a heap out-of-bounds write whose offset\nis attacker-chosen and whose contents come from the device. The\nper-field guard in cx231xx_copy_vbi_line() does not help: it bounds the\ncopy against the latched lines_per_field, not the plane\u0027s real capacity,\nand vb2 does not re-run buf_prepare() for an already prepared buffer.\n\nRefuse the format/standard change when the VBI queue is busy as well, so\nthe geometry cannot change underneath an allocated VBI buffer."
        }
      ],
      "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 overflow is reached only through local V4L2 ioctls (VIDIOC_S_FMT/VIDIOC_S_STD plus REQBUFS/QBUF/STREAMON) on the cx231xx /dev/videoN and /dev/vbiN nodes. A USB capture stick being present is a hardware precondition; the attacker does not inject USB packets, so the path is Local rather than Physical.\nAC:L - The attacker fully controls the sequence: shrink width via VIDIOC_S_FMT, allocate a small VBI plane, STREAMON, then enlarge width or switch standard on the video node while only vidq was checked. Subsequent URB completions copy field-2 VBI with the new geometry into the old plane with no race or layout outside the attacker\u0027s control.\nPR:L - cx231xx_v4l2_open(), vidioc_s_fmt_vid_cap(), and vidioc_s_std() perform no capability checks. Triggering the bug needs only an unprivileged local user who can open the V4L2 nodes, which udev grants via the video group and uaccess/logind (or the Android camera context), not init-namespace root.\nUI:N - The attacking process opens /dev/videoN and /dev/vbiN and issues the ioctl sequence itself. No separate victim action such as plugging in a device, mounting a filesystem, or running a privileged helper is required.\nS:U - The out-of-bounds memcpy corrupts kernel vmalloc memory belonging to the same host kernel. Impact is local privilege-escalation or denial of service within one security authority, not a VM escape, IOMMU bypass, or other cross-boundary effect.\nC:H - cx231xx_do_vbi_copy() memcpy()s past the undersized VBI plane at an attacker-chosen offset derived from the new width and latched lines_per_field. That heap out-of-bounds write can smash adjacent vmalloc objects and is leverageable for a kernel read primitive.\nI:H - The same attacker-chosen-offset heap out-of-bounds write overwrites kernel memory after the VBI buffer on every field-2 URB completion. An out-of-bounds write of this form is sufficient for control-flow hijacking and an arbitrary write primitive.\nA:H - memcpy() past the allocated VBI plane faults on a vmalloc guard page or corrupts adjacent kernel memory, producing a kernel oops or panic from URB completion context and taking down the host."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T08:54:27.208Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/aa3314506deb9703bcf0e889db08959440228fbf"
        },
        {
          "url": "https://git.kernel.org/stable/c/90d50648af36a1fbf5dbc99238de6fd0e58a13e0"
        },
        {
          "url": "https://git.kernel.org/stable/c/a5dd3d7fba358ff9486f3f51b2a9038348c0970a"
        },
        {
          "url": "https://git.kernel.org/stable/c/54ac6df8b8d97eddc3ae97fd2045bdedc8541b6d"
        },
        {
          "url": "https://git.kernel.org/stable/c/1d1079db8d1807e259a1d2679ed314949797aad9"
        },
        {
          "url": "https://git.kernel.org/stable/c/7087bef6510c7df5df0b19192633b8ecc0f33a6f"
        },
        {
          "url": "https://git.kernel.org/stable/c/a636c72c7f522d984fa498fc0631f33a2d0be3fd"
        },
        {
          "url": "https://git.kernel.org/stable/c/627a121c15fe05a541f44d86016294b80bada75d"
        }
      ],
      "title": "media: cx231xx: reject geometry changes while the VBI queue is busy",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89894",
    "datePublished": "2026-09-16T10:31:56.101Z",
    "dateReserved": "2026-09-11T19:38:34.773Z",
    "dateUpdated": "2026-10-19T08:54:27.208Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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