CVE-2026-90153 (GCVE-0-2026-90153)
Vulnerability from cvelistv5
Published
2026-09-17 16:06
Modified
2026-10-19 08:58
Severity ?
8.1 (High) - CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
Summary
In the Linux kernel, the following vulnerability has been resolved: ksmbd: bound smb_check_perm_dacl() ACE walks by DACL size smb_check_perm_dacl() validates that the DACL fits inside the NT security descriptor, but then bounds its two ACE walks by the remaining NTSD length (acl_size) rather than the DACL's declared size (pdacl_size). When pdacl->size is smaller than the trailing NTSD buffer, bytes after the declared DACL boundary - still inside the stored security descriptor - are parsed as ACEs during access checks. A crafted DACL can place an access-granting ACE beyond pdacl->size, and the current code accepts it during SMB2_CREATE access validation, while parse_dacl() and smb_inherit_dacl() stop at pdacl_size. Bound both ACE walks by pdacl_size to match the DACL boundary semantics used elsewhere in the server. Validation: - semantic KUnit harness shows the post-boundary ACE is selected before the fix and rejected (EACCES) after it - linux master (7.2-rc6), x86_64
References
Impacted products
Vendor Product Version
Linux Linux Version: 8f0541186e9ad1b62accc9519cc2b7a7240272a7
Version: 8f0541186e9ad1b62accc9519cc2b7a7240272a7
Version: 8f0541186e9ad1b62accc9519cc2b7a7240272a7
Version: 8f0541186e9ad1b62accc9519cc2b7a7240272a7
Version: 8f0541186e9ad1b62accc9519cc2b7a7240272a7
Version: cb69d4d6f709f87c94afa28ae64c501576692171
Version: 6e8f4abf584253cbaa596ea4ad13110cf61cd4c9
Version: 8e33102309bd6839b2e2e158f93a7b378cb4655d
Version: 5.15.62   ≤
Version: 5.18.18   ≤
Version: 5.19.2   ≤
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{
  "containers": {
    "cna": {
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        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/server/smbacl.c"
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          "product": "Linux",
          "programFiles": [
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          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "version": "6.0"
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              "status": "unaffected",
              "version": "0",
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              "version": "6.6.157",
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              "status": "unaffected",
              "version": "6.12.110",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.52",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.6",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
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              "cpeMatch": [
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                  "versionEndExcluding": "6.6.157",
                  "versionStartIncluding": "6.0",
                  "vulnerable": true
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                  "versionEndExcluding": "6.12.110",
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: bound smb_check_perm_dacl() ACE walks by DACL size\n\nsmb_check_perm_dacl() validates that the DACL fits inside the NT\nsecurity descriptor, but then bounds its two ACE walks by the\nremaining NTSD length (acl_size) rather than the DACL\u0027s declared\nsize (pdacl_size).\n\nWhen pdacl-\u003esize is smaller than the trailing NTSD buffer, bytes\nafter the declared DACL boundary - still inside the stored security\ndescriptor - are parsed as ACEs during access checks.  A crafted\nDACL can place an access-granting ACE beyond pdacl-\u003esize, and the\ncurrent code accepts it during SMB2_CREATE access validation, while\nparse_dacl() and smb_inherit_dacl() stop at pdacl_size.\n\nBound both ACE walks by pdacl_size to match the DACL boundary\nsemantics used elsewhere in the server.\n\nValidation:\n- semantic KUnit harness shows the post-boundary ACE is selected\n  before the fix and rejected (EACCES) after it\n- linux master (7.2-rc6), x86_64"
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 8.1,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The crafted NTSD is carried in SMB2_SET_INFO (SMB2_O_INFO_SECURITY) or an SMB2_CREATE SMB2_CREATE_SD_BUFFER context; set_info_sec()/ksmbd_vfs_set_sd_xattr() store that buffer, and a later SMB2_CREATE in smb2_open() loads it into smb_check_perm_dacl() from ksmbd_conn_handler_loop() on TCP/445.\nAC:L - The attacker sets pdacl-\u003esize smaller than the NTSD tail, inflates num_aces, and places an ACCESS_ALLOWED ACE after the declared DACL; smb_check_perm_dacl() then walks those bytes on the next SMB2_CREATE with no race or attacker-uncontrollable layout.\nPR:L - __handle_ksmbd_work() requires check_user_session()/get_ksmbd_tcon() before smb2_open()/smb2_set_info(); planting the NTSD needs FILE_WRITE_DAC/FILE_WRITE_OWNER in smb2_set_info_sec() or create rights for SMB2_CREATE_SD_BUFFER on an acl-xattr share, not a pre-auth path.\nUI:N - The attacker alone sends the SMB2_SET_INFO or SMB2_CREATE SD_BUFFER that stores the NTSD and the SMB2_CREATE that calls smb_check_perm_dacl(); no victim mount, open, or other interactive step is required.\nS:U - smb_check_perm_dacl() only mis-evaluates the stored DACL for ksmbd file opens; the resulting access grant stays inside the kernel SMB server and does not cross a VM, IOMMU, or sandbox boundary.\nC:H - The SID-matching ACE walk in smb_check_perm_dacl() can select a post-pdacl-\u003esize ACCESS_ALLOWED ACE for the caller or Everyone and apply its access_req, so SMB2_CREATE is authorized for FILE_READ_DATA that the declared DACL would have denied with -EACCES.\nI:H - The same extra ACE supplies attacker-controlled ace-\u003eaccess_req; ACCESS_ALLOWED with FILE_WRITE_DATA/GENERIC_ALL makes smb_check_perm_dacl() accept a write SMB2_CREATE that parse_dacl() and smb_inherit_dacl() never grant from the bounded DACL.\nA:N - Both walks stay inside the NTSD (acl_size from pntsd_size); the bug only returns success instead of -EACCES and does not oops, panic, hang, or corrupt memory."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T08:58:52.173Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/a2051ffe452afad52f580b85a3fd8851933b1e7c"
        },
        {
          "url": "https://git.kernel.org/stable/c/a29f57a14c939586d84d7fd6a029bd1fd170098f"
        },
        {
          "url": "https://git.kernel.org/stable/c/a4a307d149327dad5fb25187e1b03cebd1b04de6"
        },
        {
          "url": "https://git.kernel.org/stable/c/8e4f75e979c1d9a51b0a48ac33d0cfd5f039ec67"
        },
        {
          "url": "https://git.kernel.org/stable/c/79decd88dd3f0d42e7fb0689b1a7853bfa302459"
        }
      ],
      "title": "ksmbd: bound smb_check_perm_dacl() ACE walks by DACL size",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-90153",
    "datePublished": "2026-09-17T16:06:46.296Z",
    "dateReserved": "2026-09-11T19:38:34.789Z",
    "dateUpdated": "2026-10-19T08:58:52.173Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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