CVE-2026-93786 (GCVE-0-2026-93786)
Vulnerability from cvelistv5
Published
2026-09-24 16:02
Modified
2026-10-03 10:57
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: 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.
References
Impacted products
Vendor Product Version
Linux Linux Version: f44158485826c076335d6860d35872271a83791d
Version: f44158485826c076335d6860d35872271a83791d
Version: f44158485826c076335d6860d35872271a83791d
Version: f44158485826c076335d6860d35872271a83791d
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/server/vfs.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "4a19bb1c45667f5a5f6eff9cf6648e0f692d046f",
              "status": "affected",
              "version": "f44158485826c076335d6860d35872271a83791d",
              "versionType": "git"
            },
            {
              "lessThan": "591acf171644de590cda245fd8595b473a1beb70",
              "status": "affected",
              "version": "f44158485826c076335d6860d35872271a83791d",
              "versionType": "git"
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              "status": "affected",
              "version": "f44158485826c076335d6860d35872271a83791d",
              "versionType": "git"
            },
            {
              "lessThan": "e148e567a9252643baa125cb65d7ae9c2c6cf68a",
              "status": "affected",
              "version": "f44158485826c076335d6860d35872271a83791d",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/server/vfs.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": "6.6.158",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.111",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.53",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.6.158",
                  "versionStartIncluding": "5.15",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.111",
                  "versionStartIncluding": "5.15",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.53",
                  "versionStartIncluding": "5.15",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2",
                  "versionStartIncluding": "5.15",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "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": "2026-10-03T10:57:21.384Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/4a19bb1c45667f5a5f6eff9cf6648e0f692d046f"
        },
        {
          "url": "https://git.kernel.org/stable/c/591acf171644de590cda245fd8595b473a1beb70"
        },
        {
          "url": "https://git.kernel.org/stable/c/0093909becbda22b62b39b654dbc607faed59cd0"
        },
        {
          "url": "https://git.kernel.org/stable/c/e148e567a9252643baa125cb65d7ae9c2c6cf68a"
        }
      ],
      "title": "ksmbd: preserve VFS inherited POSIX ACL mask",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-93786",
    "datePublished": "2026-09-24T16:02:19.798Z",
    "dateReserved": "2026-09-18T17:59:28.788Z",
    "dateUpdated": "2026-10-03T10:57:21.384Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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