FKIE_CVE-2026-63909

Vulnerability from fkie_nvd - Published: 2026-07-19 16:17 - Updated: 2026-07-20 15:16
Severity
8.1 (High) - CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: ksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops Commit d07b26f39246 ("ksmbd: require minimum ACE size in smb_check_perm_dacl()") introduced a transposed bounds check: if (offsetof(struct smb_ace, sid) + aces_size < CIFS_SID_BASE_SIZE) Since offsetof(..sid) is 8 and CIFS_SID_BASE_SIZE is 8, this evaluates to `aces_size < 0`. Because `aces_size` is always non-negative, this check becomes dead code and never breaks the loop. Worse, that commit removed the old 4-byte guard, meaning the loop now reads `ace->size` (offset 2) even when `aces_size` is 0-3 bytes. This re-opens a 2-byte heap out-of-bounds (OOB) read past the pntsd allocation during subsequent SMB2_CREATE operations. Fix this by properly transposing the comparison to require at least 16 bytes (8-byte offset + 8-byte SID base), matching the correct form used in smb_inherit_dacl().
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/0e60dafe97eca61721f3db456f97d97a80c6c8ae
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/0fe08c5776a798f46df1fd74b331be26bdd644d6
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/4f7c131d2bdd7cd64b96f60d10be5ea72253f520
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/5500ba1d410aed1eded3eb04a76b10cfb4409334
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/94215d55b09445993929f4fc966061d61de74929
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/d333af32e4451285e427f2d9c29de3a39f6f6d48
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/f6324b4240cf0b26a84c33f68a1222d727ff4af2
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/server/smbacl.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "5500ba1d410aed1eded3eb04a76b10cfb4409334",
              "status": "affected",
              "version": "282cbbb476b9f35793452bc461934af4c7eca169",
              "versionType": "git"
            },
            {
              "lessThan": "f6324b4240cf0b26a84c33f68a1222d727ff4af2",
              "status": "affected",
              "version": "f20adc4ef7428bc485ee83fd1a592252fb87718b",
              "versionType": "git"
            },
            {
              "lessThan": "0fe08c5776a798f46df1fd74b331be26bdd644d6",
              "status": "affected",
              "version": "325d4ac11f526cb8964cff14548ccf02d8c756d8",
              "versionType": "git"
            },
            {
              "lessThan": "d333af32e4451285e427f2d9c29de3a39f6f6d48",
              "status": "affected",
              "version": "95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c",
              "versionType": "git"
            },
            {
              "lessThan": "94215d55b09445993929f4fc966061d61de74929",
              "status": "affected",
              "version": "90089584b2e25c4510b7b987387b4405f0673ece",
              "versionType": "git"
            },
            {
              "lessThan": "4f7c131d2bdd7cd64b96f60d10be5ea72253f520",
              "status": "affected",
              "version": "151b1799861fde38087c08f613abc2843ef597b0",
              "versionType": "git"
            },
            {
              "lessThan": "0e60dafe97eca61721f3db456f97d97a80c6c8ae",
              "status": "affected",
              "version": "d07b26f39246a82399661936dd0c853983cfade7",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/server/smbacl.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "6.6.143",
              "status": "affected",
              "version": "6.6.140",
              "versionType": "semver"
            },
            {
              "lessThan": "6.12.93",
              "status": "affected",
              "version": "6.12.84",
              "versionType": "semver"
            },
            {
              "lessThan": "6.18.35",
              "status": "affected",
              "version": "6.18.25",
              "versionType": "semver"
            },
            {
              "lessThan": "7.0.12",
              "status": "affected",
              "version": "7.0.2",
              "versionType": "semver"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops\n\nCommit d07b26f39246 (\"ksmbd: require minimum ACE size in\nsmb_check_perm_dacl()\") introduced a transposed bounds check:\n\n    if (offsetof(struct smb_ace, sid) + aces_size \u003c CIFS_SID_BASE_SIZE)\n\nSince offsetof(..sid) is 8 and CIFS_SID_BASE_SIZE is 8, this evaluates\nto `aces_size \u003c 0`. Because `aces_size` is always non-negative, this\ncheck becomes dead code and never breaks the loop.\n\nWorse, that commit removed the old 4-byte guard, meaning the loop now\nreads `ace-\u003esize` (offset 2) even when `aces_size` is 0-3 bytes. This\nre-opens a 2-byte heap out-of-bounds (OOB) read past the pntsd allocation\nduring subsequent SMB2_CREATE operations.\n\nFix this by properly transposing the comparison to require at least\n16 bytes (8-byte offset + 8-byte SID base), matching the correct form\nused in smb_inherit_dacl()."
    }
  ],
  "id": "CVE-2026-63909",
  "lastModified": "2026-07-20T15:16:54.933",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "HIGH",
          "baseScore": 8.1,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "NONE",
          "privilegesRequired": "LOW",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 2.8,
        "impactScore": 5.2,
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-07-19T16:17:08.747",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/0e60dafe97eca61721f3db456f97d97a80c6c8ae"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/0fe08c5776a798f46df1fd74b331be26bdd644d6"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/4f7c131d2bdd7cd64b96f60d10be5ea72253f520"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/5500ba1d410aed1eded3eb04a76b10cfb4409334"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/94215d55b09445993929f4fc966061d61de74929"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/d333af32e4451285e427f2d9c29de3a39f6f6d48"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/f6324b4240cf0b26a84c33f68a1222d727ff4af2"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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