HighFix available

smb: client: validate the whole DACL before rewriting it in cifsacl

Type: advisorySources: OSV

In the Linux kernel, the following vulnerability has been resolved: smb: client: validate the whole DACL before rewriting it in cifsacl build_sec_desc() and id_mode_to_cifs_acl() derive a DACL pointer from a server-supplied dacloffset and then use the incoming ACL to rebuild the chmod/chown security descriptor. The original fix only checked that the struct smb_acl header fits before reading dacl_ptr->size or dacl_ptr->num_aces. That avoids the immediate header-field OOB read, but the rewrite helpers still walk ACEs based on pdacl->num_aces with no structural validation of the incoming DACL body. A malicious server can return a truncated DACL that still contains a header, claims one or more ACEs, and then drive replace_sids_and_copy_aces() or set_chmod_dacl() past the validated extent while they compare or copy attacker-controlled ACEs. Factor the DACL structural checks into validate_dacl(), extend them to validate each ACE against the DACL bounds, and use the shared validator before the chmod/chown rebuild paths. parse_dacl() reuses the same validator so the read-side parser and write-side rewrite paths agree on what constitutes a well-formed incoming DACL.

Products: Kernel
Affected versions: Not specified
Fixed versions: 5.15.210, 6.1.176, 6.12.86, 6.18.35, 6.6.140, 7.0.2
CVEs: CVE-2026-31709
Confirmed fixed CVEs: Not specified
Updated in this feed: 4 Nov 2026, 18:40 UTC · Revision 1

Source evidence

smb: client: validate the whole DACL before rewriting it in cifsacl

core-osv · Original source

Published 1 May 2026, 13:56 UTC

osv:CVE-2026-31709

Kernel

Fixed versions: 5.15.210, 6.1.176, 6.6.140, 6.12.86, 6.18.35, 7.0.2

Complete source record

{
  "id": "74646bbef46265801f999cee9bf3b624fa1e134c1f640323235a7863f0cf48a3",
  "url": "https://osv.dev/vulnerability/CVE-2026-31709",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "smb: client: validate the whole DACL before rewriting it in cifsacl",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: smb: client: validate the whole DACL before rewriting it in cifsacl build_sec_desc() and id_mode_to_cifs_acl() derive a DACL pointer from a server-supplied dacloffset and then use the incoming ACL to rebuild the chmod/chown security descriptor. The original fix only checked that the struct smb_acl header fits before reading dacl_ptr->size or dacl_ptr->num_aces. That avoids the immediate header-field OOB read, but the rewrite helpers still walk ACEs based on pdacl->num_aces with no structural validation of the incoming DACL body. A malicious server can return a truncated DACL that still contains a header, claims one or more ACEs, and then drive replace_sids_and_copy_aces() or set_chmod_dacl() past the validated extent while they compare or copy attacker-controlled ACEs. Factor the DACL structural checks into validate_dacl(), extend them to validate each ACE against the DACL bounds, and use the shared validator before the chmod/chown rebuild paths. parse_dacl() reuses the same validator so the read-side parser and write-side rewrite paths agree on what constitutes a well-formed incoming DACL.",
    "evidence": "osv:CVE-2026-31709",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "5.15.210",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.1.176",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.6.140",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.12.86",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.35",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "7.0.2",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-31709",
      "aliases": [
        "CVE-2026-31709"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "bc3e9dd9d104ca1b75644eab87b38ce8a924aef4"
                },
                {
                  "fixed": "b8603d9ae6c9087662b098619996bc4a8064319d"
                },
                {
                  "fixed": "c2abdebf72000a64603ced84d36ccbd164f11391"
                },
                {
                  "fixed": "8e47d297e7cf9a6029a0d38e7b22faba7d7aaf12"
                },
                {
                  "fixed": "d92f3f0b22414e7515696a02224d0af55e3004a3"
                },
                {
                  "fixed": "ff0ca46b13b9ef6edbcd238a3b6caacfef8ba0e5"
                },
                {
                  "fixed": "b78db9bddc84136f6a0bb49e8883cf200dfb87a8"
                },
                {
                  "fixed": "0a8cf165566ba55a39fd0f4de172119dd646d39a"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-31709.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.12.0"
                },
                {
                  "fixed": "5.15.210"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.16.0"
                },
                {
                  "fixed": "6.1.176"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.2.0"
                },
                {
                  "fixed": "6.6.140"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.7.0"
                },
                {
                  "fixed": "6.12.86"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.18.35"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
                },
                {
                  "fixed": "7.0.2"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-31709.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:38.222857098Z",
      "provider": "osv",
      "references": [
        "https://cert-portal.siemens.com/productcert/html/ssa-784472.html",
        "https://git.kernel.org/stable/c/0a8cf165566ba55a39fd0f4de172119dd646d39a",
        "https://git.kernel.org/stable/c/8e47d297e7cf9a6029a0d38e7b22faba7d7aaf12",
        "https://git.kernel.org/stable/c/b78db9bddc84136f6a0bb49e8883cf200dfb87a8",
        "https://git.kernel.org/stable/c/b8603d9ae6c9087662b098619996bc4a8064319d",
        "https://git.kernel.org/stable/c/c2abdebf72000a64603ced84d36ccbd164f11391",
        "https://git.kernel.org/stable/c/d92f3f0b22414e7515696a02224d0af55e3004a3",
        "https://git.kernel.org/stable/c/ff0ca46b13b9ef6edbcd238a3b6caacfef8ba0e5",
        "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-31709.json",
        "https://access.redhat.com/errata/RHSA-2026:21556",
        "https://access.redhat.com/errata/RHSA-2026:21706",
        "https://access.redhat.com/errata/RHSA-2026:21745",
        "https://access.redhat.com/errata/RHSA-2026:22900",
        "https://access.redhat.com/errata/RHSA-2026:22940",
        "https://access.redhat.com/errata/RHSA-2026:23224",
        "https://access.redhat.com/errata/RHSA-2026:23237",
        "https://access.redhat.com/errata/RHSA-2026:23329",
        "https://access.redhat.com/errata/RHSA-2026:24343",
        "https://access.redhat.com/security/cve/CVE-2026-31709",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31709.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-31709",
        "https://bugzilla.redhat.com/show_bug.cgi?id=2464476",
        "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-2026-31709.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-31709",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 505784,
  "published_at": "2026-05-01T13:56:06.522+00:00"
}