FKIE_CVE-2026-68100

Vulnerability from fkie_nvd - Published: 2026-08-10 13:19 - Updated: 2026-08-17 05:18
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: validate num_subauth when copying ACE in set_ntacl_dacl set_ntacl_dacl() copies each ACE from the attacker-controlled stored security descriptor verbatim into the response DACL without checking sid.num_subauth. The ACE bytes (including an unchecked num_subauth) originate from an authenticated SMB2_SET_INFO(SecInfo=DACL) that is stored raw via ksmbd_vfs_set_sd_xattr(); parse_dacl() rejects a bad ACE with `break` rather than an error, so parse_sec_desc() still returns success and the malformed SD reaches the xattr intact. On a subsequent SMB2_QUERY_INFO(SecInfo=DACL) for an inode carrying a POSIX access ACL, build_sec_desc() -> set_ntacl_dacl() -> set_posix_acl_entries_dacl() walks the copied ACEs and reads ntace->sid.sub_auth[ntace->sid.num_subauth - 1] with num_subauth taken straight from the stored SD. Since sub_auth[] is fixed at SID_MAX_SUB_AUTHORITIES (15), a crafted num_subauth (e.g. 255) drives an out-of-bounds heap read of ~1 KB with an offset fully controlled by an authenticated client. The sibling functions already gate this field: parse_dacl() -- num_subauth == 0 || > SID_MAX_SUB_AUTHORITIES parse_sid() -- num_subauth > SID_MAX_SUB_AUTHORITIES smb_copy_sid() -- min_t(u8, num_subauth, SID_MAX_SUB_AUTHORITIES) set_ntacl_dacl() is the lone inconsistent path that omits the check. Add the same num_subauth validation in set_ntacl_dacl() before copying the ACE, matching the gate already enforced by parse_dacl().
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/47f0b34f6bc98ed85bfdc293e8f3e432ec24958d
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/5acbd3012fd4a7ccfebd91ea6f784120084eb897
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/b6d3cc6a524416dfdb2b47e4bba2e7e20011d056
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/e31fada5143784bc05c7ae44c79eed9b7a2e147e
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/fb3dc8e6da46a1ccad1956cda57de29d9b3033e0
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": "e31fada5143784bc05c7ae44c79eed9b7a2e147e",
              "status": "affected",
              "version": "e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9",
              "versionType": "git"
            },
            {
              "lessThan": "fb3dc8e6da46a1ccad1956cda57de29d9b3033e0",
              "status": "affected",
              "version": "e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9",
              "versionType": "git"
            },
            {
              "lessThan": "b6d3cc6a524416dfdb2b47e4bba2e7e20011d056",
              "status": "affected",
              "version": "e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9",
              "versionType": "git"
            },
            {
              "lessThan": "5acbd3012fd4a7ccfebd91ea6f784120084eb897",
              "status": "affected",
              "version": "e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9",
              "versionType": "git"
            },
            {
              "lessThan": "47f0b34f6bc98ed85bfdc293e8f3e432ec24958d",
              "status": "affected",
              "version": "e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/server/smbacl.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "5.15"
            },
            {
              "lessThan": "5.15",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.148",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.101",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.42",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.6",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: validate num_subauth when copying ACE in set_ntacl_dacl\n\nset_ntacl_dacl() copies each ACE from the attacker-controlled stored\nsecurity descriptor verbatim into the response DACL without checking\nsid.num_subauth. The ACE bytes (including an unchecked num_subauth)\noriginate from an authenticated SMB2_SET_INFO(SecInfo=DACL) that is\nstored raw via ksmbd_vfs_set_sd_xattr(); parse_dacl() rejects a bad ACE\nwith `break` rather than an error, so parse_sec_desc() still returns\nsuccess and the malformed SD reaches the xattr intact.\n\nOn a subsequent SMB2_QUERY_INFO(SecInfo=DACL) for an inode carrying a\nPOSIX access ACL, build_sec_desc() -\u003e set_ntacl_dacl() -\u003e\nset_posix_acl_entries_dacl() walks the copied ACEs and reads\n\n    ntace-\u003esid.sub_auth[ntace-\u003esid.num_subauth - 1]\n\nwith num_subauth taken straight from the stored SD. Since sub_auth[]\nis fixed at SID_MAX_SUB_AUTHORITIES (15), a crafted num_subauth (e.g.\n255) drives an out-of-bounds heap read of ~1 KB with an offset fully\ncontrolled by an authenticated client.\n\nThe sibling functions already gate this field:\n  parse_dacl()    -- num_subauth == 0 || \u003e SID_MAX_SUB_AUTHORITIES\n  parse_sid()     -- num_subauth \u003e SID_MAX_SUB_AUTHORITIES\n  smb_copy_sid()  -- min_t(u8, num_subauth, SID_MAX_SUB_AUTHORITIES)\nset_ntacl_dacl() is the lone inconsistent path that omits the check.\n\nAdd the same num_subauth validation in set_ntacl_dacl() before copying\nthe ACE, matching the gate already enforced by parse_dacl()."
    }
  ],
  "id": "CVE-2026-68100",
  "lastModified": "2026-08-17T05:18:09.407",
  "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": "2026-08-10T13:19:54.533",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/47f0b34f6bc98ed85bfdc293e8f3e432ec24958d"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/5acbd3012fd4a7ccfebd91ea6f784120084eb897"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/b6d3cc6a524416dfdb2b47e4bba2e7e20011d056"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/e31fada5143784bc05c7ae44c79eed9b7a2e147e"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/fb3dc8e6da46a1ccad1956cda57de29d9b3033e0"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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