CVE-2026-64394 (GCVE-0-2026-64394)
Vulnerability from cvelistv5
Published
2026-07-25 08:50
Modified
2026-08-17 04:54
Severity ?
8.8 (High) - CVSS:3.1/AV:N/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: ksmbd: add a WRITE_DAC/WRITE_OWNER check to SMB2 SET_INFO SECURITY commit cc57232cae23 ("ksmbd: fix FSCTL permission bypass by adding a permission check for FSCTL_SET_SPARSE") added a fp->daccess gate to fsctl_set_sparse and noted that "similar handle-level checks exist in other functions but are missing here." The SMB2 SET_INFO SECURITY arm is one of the missing ones, and the most security-relevant: smb2_set_info_sec() calls set_info_sec() with no per-handle access check. set_info_sec() (fs/smb/server/smbacl.c) re-permissions the file: it rewrites owner/group/mode via notify_change(), rewrites the POSIX ACL via set_posix_acl(), and on KSMBD_SHARE_FLAG_ACL_XATTR shares removes and rewrites the Windows security descriptor via ksmbd_vfs_set_sd_xattr(). Every other persistent-mutation arm of the sibling handler smb2_set_info_file() checks fp->daccess first (FILE_WRITE_DATA / FILE_DELETE / FILE_WRITE_EA / FILE_WRITE_ATTRIBUTES); the SECURITY arm — which mutates the access control itself — is the only one with no gate. A client can therefore open a handle with FILE_WRITE_ATTRIBUTES only (no FILE_WRITE_DAC / FILE_WRITE_OWNER) and use SMB2_SET_INFO with InfoType SMB2_O_INFO_SECURITY to rewrite the file's DACL and owner, granting itself access the handle's daccess never carried. Unlike the FSCTL data arms this is a metadata/xattr operation, so there is no FMODE_WRITE VFS backstop — the missing fp->daccess check is the entire gate. Setting a security descriptor is the WRITE_DAC / WRITE_OWNER operation, so require at least one of those on the handle before re-permissioning the file. -EACCES is mapped to STATUS_ACCESS_DENIED by smb2_set_info().
References
Impacted products
Vendor Product Version
Linux Linux Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
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{
  "containers": {
    "cna": {
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        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/server/smb2pdu.c"
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          "product": "Linux",
          "programFiles": [
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          "vendor": "Linux",
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              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.96",
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              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.39",
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              "lessThanOrEqual": "7.1.*",
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              "version": "7.1.4",
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            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.1.178",
                  "versionStartIncluding": "5.15",
                  "vulnerable": true
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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\nksmbd: add a WRITE_DAC/WRITE_OWNER check to SMB2 SET_INFO SECURITY\n\ncommit cc57232cae23 (\"ksmbd: fix FSCTL permission bypass by adding a\npermission check for FSCTL_SET_SPARSE\") added a fp-\u003edaccess gate to\nfsctl_set_sparse and noted that \"similar handle-level checks exist in other\nfunctions but are missing here.\" The SMB2 SET_INFO SECURITY arm is one of\nthe missing ones, and the most security-relevant: smb2_set_info_sec() calls\nset_info_sec() with no per-handle access check.\n\nset_info_sec() (fs/smb/server/smbacl.c) re-permissions the file: it\nrewrites owner/group/mode via notify_change(), rewrites the POSIX ACL via\nset_posix_acl(), and on KSMBD_SHARE_FLAG_ACL_XATTR shares removes and\nrewrites the Windows security descriptor via ksmbd_vfs_set_sd_xattr().\nEvery other persistent-mutation arm of the sibling handler\nsmb2_set_info_file() checks fp-\u003edaccess first (FILE_WRITE_DATA /\nFILE_DELETE / FILE_WRITE_EA / FILE_WRITE_ATTRIBUTES); the SECURITY arm \u2014\nwhich mutates the access control itself \u2014 is the only one with no gate.\n\nA client can therefore open a handle with FILE_WRITE_ATTRIBUTES only (no\nFILE_WRITE_DAC / FILE_WRITE_OWNER) and use SMB2_SET_INFO with InfoType\nSMB2_O_INFO_SECURITY to rewrite the file\u0027s DACL and owner, granting itself\naccess the handle\u0027s daccess never carried. Unlike the FSCTL data arms this\nis a metadata/xattr operation, so there is no FMODE_WRITE VFS backstop \u2014\nthe missing fp-\u003edaccess check is the entire gate.\n\nSetting a security descriptor is the WRITE_DAC / WRITE_OWNER operation, so\nrequire at least one of those on the handle before re-permissioning the\nfile. -EACCES is mapped to STATUS_ACCESS_DENIED by smb2_set_info()."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 8.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The vulnerable SMB2 SET_INFO handler is remotely reachable through ksmbd over TCP port 445.\nAC:L - An attacker can deterministically open an attribute-only handle and submit a crafted security descriptor, with no race or uncontrollable condition.\nPR:L - A valid SMB session, writable tree connection, and permission to open the target with FILE_WRITE_ATTRIBUTES are required, but no administrative privileges are needed.\nUI:N - The attacker directly sends the SMB requests without requiring any victim action.\nS:U - The bypass affects files governed by the same host and ksmbd share security authority and does not cross a virtualization or sandbox boundary.\nC:H - The attacker can rewrite the DACL and mode to grant read access, potentially disclosing complete protected files within the share.\nI:H - The attacker can grant itself write or delete rights and subsequently modify or destroy protected file contents, ownership metadata, and ACLs.\nA:H - The attacker can deny legitimate access or grant itself sufficient rights to corrupt or destroy affected share data, causing complete loss of availability for those resources."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T04:54:47.889Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/0848b1d8b403f530878195dcbe241a2fddb9d0e1"
        },
        {
          "url": "https://git.kernel.org/stable/c/e6aa731f1b4b3e08caebf66a99f04b22bdab2e99"
        },
        {
          "url": "https://git.kernel.org/stable/c/9ab2ffd3ed3d4ca1667c52de27026ddabc11e537"
        },
        {
          "url": "https://git.kernel.org/stable/c/f56535db508ead8dec1c481ad93d7d8acd8f8f1e"
        },
        {
          "url": "https://git.kernel.org/stable/c/aae600cdaffc6d9ce97645f129799a103a97d06d"
        },
        {
          "url": "https://git.kernel.org/stable/c/44df157a1183a7f746caa970c169255da5ac61f8"
        }
      ],
      "title": "ksmbd: add a WRITE_DAC/WRITE_OWNER check to SMB2 SET_INFO SECURITY",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-64394",
    "datePublished": "2026-07-25T08:50:39.797Z",
    "dateReserved": "2026-07-19T15:36:31.785Z",
    "dateUpdated": "2026-08-17T04:54:47.889Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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