CVE-2026-93786 (GCVE-0-2026-93786)

Vulnerability from cvelistv5 – Published: 2026-09-24 16:02 – Updated: 2026-09-25 12:42
VLAI
Title
ksmbd: preserve VFS inherited POSIX ACL mask
Summary
In the Linux kernel, the following vulnerability has been resolved: ksmbd: preserve VFS inherited POSIX ACL mask The VFS initializes a child's POSIX ACL from the parent's default ACL and the requested creation mode. Do not mutate the parent ACL or overwrite the child's VFS-computed access and default ACLs afterwards. This preserves restrictive ACL_MASK entries and prevents SMB object creation from widening effective permissions.
Severity
8.1 (High)
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: f44158485826c076335d6860d35872271a83791d , < 591acf171644de590cda245fd8595b473a1beb70 (git)
Affected: f44158485826c076335d6860d35872271a83791d , < 0093909becbda22b62b39b654dbc607faed59cd0 (git)
Affected: f44158485826c076335d6860d35872271a83791d , < e148e567a9252643baa125cb65d7ae9c2c6cf68a (git)
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Linux Linux Affected: 5.15
Unaffected: 0 , < 5.15 (semver)
Unaffected: 6.12.111 , ≤ 6.12.* (semver)
Unaffected: 6.18.53 , ≤ 6.18.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/server/vfs.c"
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          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
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              "status": "affected",
              "version": "f44158485826c076335d6860d35872271a83791d",
              "versionType": "git"
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              "versionType": "git"
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          "vendor": "Linux",
          "versions": [
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              "status": "affected",
              "version": "5.15"
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              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
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              "status": "unaffected",
              "version": "6.12.111",
              "versionType": "semver"
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            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.53",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
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        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
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                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.111",
                  "versionStartIncluding": "5.15",
                  "vulnerable": true
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              "operator": "OR"
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: preserve VFS inherited POSIX ACL mask\n\nThe VFS initializes a child\u0027s POSIX ACL from the parent\u0027s default ACL and\nthe requested creation mode. Do not mutate the parent ACL or overwrite the\nchild\u0027s VFS-computed access and default ACLs afterwards.\n\nThis preserves restrictive ACL_MASK entries and prevents SMB object creation\nfrom widening effective permissions."
        }
      ],
      "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 - SMB2 CREATE is dispatched to smb2_open() from ksmbd_conn_handler_loop() on TCP/445; after smb2_creat()/vfs_create() succeeds, smb2_open() calls ksmbd_vfs_inherit_posix_acl(), which overwrites the new object\u0027s POSIX ACL. That CREATE is the trigger; the damaged ACL then governs later SMB2 READ/WRITE.\nAC:L - ksmbd_vfs_inherit_posix_acl() does pace-\u003ee_perm=0x07 on the ACL_MASK entry of get_inode_acl(parent, ACL_TYPE_DEFAULT) then set_posix_acl()s that onto the child. A single SMB2 CREATE of a new name in a directory that already has a default POSIX ACL hits this with no race; CONFIG_FS_POSIX_ACL is the helper\u0027s own gate.\nPR:L - __handle_ksmbd_work() runs smb2_check_user_session() (SMB2_CREATE is not in the NEGOTIATE/SESSION_SETUP skip list) and smb2_get_ksmbd_tcon() before smb2_open(); that path also requires KSMBD_TREE_CONN_FLAG_WRITABLE and O_CREAT, so an authenticated share user with create rights is required, not a pre-auth client.\nUI:N - The attacking SMB client itself sends the SMB2 CREATE that makes smb2_open() call ksmbd_vfs_inherit_posix_acl() on the object it just created; no local user must mount a volume, open a file, or confirm any action.\nS:U - set_posix_acl() only replaces POSIX access/default ACL xattrs on the ksmbd-exported filesystem in this host kernel; the resulting permission widening stays in that same security authority and is not a VM escape, IOMMU bypass, or sandbox breakout.\nC:H - posix_acl_permission() grants named-user/group access as (entry.e_perm \u0026 mask.e_perm). Forcing ACL_MASK to 0x07 in ksmbd_vfs_inherit_posix_acl() drops that cap, so named principals whose default-ACL entries included ACL_READ can read new-object contents the original mask would have denied.\nI:H - The same set_posix_acl(ACL_TYPE_ACCESS) of the unmasked ACL makes ACL_WRITE in named entries effective on the new file; for directories it also writes ACL_TYPE_DEFAULT with mask 0x07, and get_inode_acl() returns the shared parent cache so the in-place e_perm store widens later inherits.\nA:N - The path stores a posix_acl_valid ACL whose ACL_MASK e_perm is 0x07 via set_posix_acl(); it does not NULL-deref, BUG, panic, hang, or leak kernel memory, so the ksmbd worker and host remain available."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-25T12:42:51.882Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
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          "url": "https://git.kernel.org/stable/c/591acf171644de590cda245fd8595b473a1beb70"
        },
        {
          "url": "https://git.kernel.org/stable/c/0093909becbda22b62b39b654dbc607faed59cd0"
        },
        {
          "url": "https://git.kernel.org/stable/c/e148e567a9252643baa125cb65d7ae9c2c6cf68a"
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      ],
      "title": "ksmbd: preserve VFS inherited POSIX ACL mask",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-93786",
    "datePublished": "2026-09-24T16:02:19.798Z",
    "dateReserved": "2026-09-18T17:59:28.788Z",
    "dateUpdated": "2026-09-25T12:42:51.882Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
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      "date": "2026-09-28",
      "epss": "0.0033",
      "percentile": "0.23601"
    },
    "microsoft_vex": {
      "current_release_date": "2026-09-27T23:45:07.000Z",
      "cve": "CVE-2026-93786",
      "id": "msrc_CVE-2026-93786",
      "initial_release_date": "2026-09-27T23:45:07.000Z",
      "product_status:known_affected": "1",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "ksmbd: preserve VFS inherited POSIX ACL mask",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-93786.json",
      "version": "1"
    },
    "nvd": {
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        "affected": [
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                "defaultStatus": "unaffected",
                "product": "Linux",
                "programFiles": [
                  "fs/smb/server/vfs.c"
                ],
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        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: preserve VFS inherited POSIX ACL mask\n\nThe VFS initializes a child\u0027s POSIX ACL from the parent\u0027s default ACL and\nthe requested creation mode. Do not mutate the parent ACL or overwrite the\nchild\u0027s VFS-computed access and default ACLs afterwards.\n\nThis preserves restrictive ACL_MASK entries and prevents SMB object creation\nfrom widening effective permissions."
          }
        ],
        "id": "CVE-2026-93786",
        "lastModified": "2026-09-25T13:17:19.157",
        "metrics": {
          "cvssMetricV31": [
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              "cvssData": {
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                "attackVector": "NETWORK",
                "availabilityImpact": "NONE",
                "baseScore": 8.1,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "LOW",
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                "userInteraction": "NONE",
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              "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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        "vulnStatus": "Received"
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      "current_release_date": "2026-09-28T10:24:01+00:00",
      "cve": "CVE-2026-93786",
      "id": "CVE-2026-93786",
      "initial_release_date": "2026-09-24T00:00:00+00:00",
      "product_status:known_not_affected": "276",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: ksmbd: preserve VFS inherited POSIX ACL mask",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-93786.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-09-25T23:48:57Z",
      "cve": "CVE-2026-93786",
      "id": "CVE-2026-93786",
      "initial_release_date": "2026-09-24T23:47:53Z",
      "product_status:known_affected": "108",
      "product_status:known_not_affected": "239",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-93786",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-93786.json",
      "version": "3"
    }
  }
}



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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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