ksmbd: require 3 sub-authorities before reading sub_auth[2]

{
  "id": "f74265407c66c1814e5dc682d6601924703930dc0e17b577827fe3775dd49131",
  "url": "https://osv.dev/vulnerability/CVE-2026-31611",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "ksmbd: require 3 sub-authorities before reading sub_auth[2]",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: ksmbd: require 3 sub-authorities before reading sub_auth[2] parse_dacl() compares each ACE SID against sid_unix_NFS_mode and on match reads sid.sub_auth[2] as the file mode. If sid_unix_NFS_mode is the prefix S-1-5-88-3 with num_subauth = 2 then compare_sids() compares only min(num_subauth, 2) sub-authorities so a client SID with num_subauth = 2 and sub_auth = {88, 3} will match. If num_subauth = 2 and the ACE is placed at the very end of the security descriptor, sub_auth[2] will be 4 bytes past end_of_acl. The out-of-band bytes will then be masked to the low 9 bits and applied as the file's POSIX mode, probably not something that is good to have happen. Fix this up by forcing the SID to actually carry a third sub-authority before reading it at all.",
    "evidence": "osv:CVE-2026-31611",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.1.175",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.6.136",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.12.83",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.24",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.19.14",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "7.0.1",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-31611",
      "aliases": [
        "CVE-2026-31611"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9"
                },
                {
                  "fixed": "cf2148b880fb7c0fcd727202dbc4fd5d6998b9c2"
                },
                {
                  "fixed": "b5b5d5936a50497fb151c0b122899a6894721c2b"
                },
                {
                  "fixed": "08f9e6d899b5c834bbcc239eae1bed58d9b15d2c"
                },
                {
                  "fixed": "d2454f4a002d08560a60f214f392e6491cf11560"
                },
                {
                  "fixed": "46bbcd3ebfb3549c8da1838fc4493e79bd3241e7"
                },
                {
                  "fixed": "9401f86a224f37b50e6a3ccf1d46a70d5ef8af0a"
                },
                {
                  "fixed": "53370cf9090777774e07fd9a8ebce67c6cc333ab"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-31611.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.15.0"
                },
                {
                  "fixed": "6.1.175"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.2.0"
                },
                {
                  "fixed": "6.6.136"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.7.0"
                },
                {
                  "fixed": "6.12.83"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.18.24"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
                },
                {
                  "fixed": "6.19.14"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.20.0"
                },
                {
                  "fixed": "7.0.1"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-31611.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:50.021503748Z",
      "provider": "osv",
      "references": [
        "https://cert-portal.siemens.com/productcert/html/ssa-784472.html",
        "https://git.kernel.org/stable/c/08f9e6d899b5c834bbcc239eae1bed58d9b15d2c",
        "https://git.kernel.org/stable/c/46bbcd3ebfb3549c8da1838fc4493e79bd3241e7",
        "https://git.kernel.org/stable/c/53370cf9090777774e07fd9a8ebce67c6cc333ab",
        "https://git.kernel.org/stable/c/9401f86a224f37b50e6a3ccf1d46a70d5ef8af0a",
        "https://git.kernel.org/stable/c/b5b5d5936a50497fb151c0b122899a6894721c2b",
        "https://git.kernel.org/stable/c/cf2148b880fb7c0fcd727202dbc4fd5d6998b9c2",
        "https://git.kernel.org/stable/c/d2454f4a002d08560a60f214f392e6491cf11560",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31611.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-31611",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31611.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-31611",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 518232,
  "published_at": "2026-04-24T14:42:32.124+00:00"
}