CVE-2026-80975

Full vulnerability record from the local CVENow database.

Description

In the Linux kernel, the following vulnerability has been resolved: mfd: qnap-mcu: keep the reply buffer alive past a command timeout qnap_mcu_exec() publishes an on-stack buffer to the receive path: unsigned char rx[QNAP_MCU_RX_BUFFER_SIZE]; ... reply->data = rx; reply->length = length; and qnap_mcu_receive_buf() writes into it from the serdev receive path, which runs out of flush_to_ldisc() and is not serialized against qnap_mcu_exec() at all. bus_lock cannot cover it, because qnap_mcu_exec() holds that mutex across wait_for_completion_timeout(). On a timeout qnap_mcu_exec() returns with reply->data still pointing at its own frame. A reply that arrives late, or an unsolicited message from the MCU, is then written into a stack frame that has been left, corrupting whatever runs next on that stack. The same applies when qnap_mcu_write() fails, since that path returns without touching the reply state either. Move the receive buffer into struct qnap_mcu. It is 37 bytes and the structure is devm_kzalloc()ed, so it lives as long as the driver, and a late write lands in memory that is still valid and is reinitialized by the next command. bus_lock keeps commands from sharing it. This deliberately does not clear reply->data or reply->length on the timeout path. Doing so races with qnap_mcu_receive_buf(), which reads both after its if (!reply->length) return size; check: clearing reply->data gives a NULL dereference, and clearing reply->length alone removes the reply->received == reply->length exit condition, so the copy loop runs until the uart chunk is consumed and overruns the buffer. Leaving both set keeps the write bounded by reply->length, which qnap_mcu_exec() has already checked against sizeof(mcu->rx).

Severity

HIGH

CVSS score

7.8 (v3.1)

Vulnerability status

Received

Source identifier

416baaa9-dc9f-4396-8d5f-8c081fb06d67

Published

2026-09-11 20:19:03.763000

Last modified

2026-10-19 09:17:29.527000

View original CVE JSON

{
  "id": "CVE-2026-80975",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "published": "2026-09-11T20:19:03.763",
  "lastModified": "2026-10-19T09:17:29.527",
  "vulnStatus": "Received",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmfd: qnap-mcu: keep the reply buffer alive past a command timeout\n\nqnap_mcu_exec() publishes an on-stack buffer to the receive path:\n\n\tunsigned char rx[QNAP_MCU_RX_BUFFER_SIZE];\n\t...\n\treply->data = rx;\n\treply->length = length;\n\nand qnap_mcu_receive_buf() writes into it from the serdev receive path,\nwhich runs out of flush_to_ldisc() and is not serialized against\nqnap_mcu_exec() at all. bus_lock cannot cover it, because qnap_mcu_exec()\nholds that mutex across wait_for_completion_timeout().\n\nOn a timeout qnap_mcu_exec() returns with reply->data still pointing at\nits own frame. A reply that arrives late, or an unsolicited message from\nthe MCU, is then written into a stack frame that has been left, corrupting\nwhatever runs next on that stack. The same applies when qnap_mcu_write()\nfails, since that path returns without touching the reply state either.\n\nMove the receive buffer into struct qnap_mcu. It is 37 bytes and the\nstructure is devm_kzalloc()ed, so it lives as long as the driver, and a\nlate write lands in memory that is still valid and is reinitialized by the\nnext command. bus_lock keeps commands from sharing it.\n\nThis deliberately does not clear reply->data or reply->length on the\ntimeout path. Doing so races with qnap_mcu_receive_buf(), which reads both\nafter its\n\n\tif (!reply->length)\n\t\treturn size;\n\ncheck: clearing reply->data gives a NULL dereference, and clearing\nreply->length alone removes the reply->received == reply->length exit\ncondition, so the copy loop runs until the uart chunk is consumed and\noverruns the buffer. Leaving both set keeps the write bounded by\nreply->length, which qnap_mcu_exec() has already checked against\nsizeof(mcu->rx)."
    }
  ],
  "affected": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "affectedData": [
        {
          "vendor": "Linux",
          "product": "Linux",
          "defaultStatus": "unaffected",
          "programFiles": [
            "drivers/mfd/qnap-mcu.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "versions": [
            {
              "version": "998f70d1806bb718a7565f350283e4a79c8cbb4b",
              "lessThan": "0b6680e306397097a97767447368221fac753809",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "998f70d1806bb718a7565f350283e4a79c8cbb4b",
              "lessThan": "8391ee06d08845a0a165b5fe679ba326915166b2",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "998f70d1806bb718a7565f350283e4a79c8cbb4b",
              "lessThan": "47504742cea7878ebd1bf1491bbed923df6b90b1",
              "versionType": "git",
              "status": "affected"
            }
          ]
        },
        {
          "vendor": "Linux",
          "product": "Linux",
          "defaultStatus": "affected",
          "programFiles": [
            "drivers/mfd/qnap-mcu.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "versions": [
            {
              "version": "6.14",
              "status": "affected"
            },
            {
              "version": "0",
              "lessThan": "6.14",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "6.18.51",
              "lessThanOrEqual": "6.18.*",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "7.2.4",
              "lessThanOrEqual": "7.2.*",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "7.3",
              "lessThanOrEqual": "*",
              "versionType": "original_commit_for_fix",
              "status": "unaffected"
            }
          ]
        }
      ]
    }
  ],
  "metrics": {
    "cvssMetricV31": [
      {
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "type": "Secondary",
        "cvssData": {
          "version": "3.1",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
          "baseScore": 7.8,
          "baseSeverity": "HIGH",
          "attackVector": "LOCAL",
          "attackComplexity": "LOW",
          "privilegesRequired": "LOW",
          "userInteraction": "NONE",
          "scope": "UNCHANGED",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "availabilityImpact": "HIGH"
        },
        "exploitabilityScore": 1.8,
        "impactScore": 5.9
      }
    ]
  },
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/0b6680e306397097a97767447368221fac753809",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/47504742cea7878ebd1bf1491bbed923df6b90b1",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/8391ee06d08845a0a165b5fe679ba326915166b2",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ]
}