{
  "affected": [
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:12",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:13",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.12.85-1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:14",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "7.0.3-1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "details": "In the Linux kernel, the following vulnerability has been resolved:  ksmbd: validate num_aces and harden ACE walk in smb_inherit_dacl()  smb_inherit_dacl() trusts the on-disk num_aces value from the parent directory's DACL xattr and uses it to size a heap allocation:    aces_base = kmalloc(sizeof(struct smb_ace) * num_aces * 2, ...);  num_aces is a u16 read from le16_to_cpu(parent_pdacl-\u003enum_aces) without checking that it is consistent with the declared pdacl_size. An authenticated client whose parent directory's security.NTACL is tampered (e.g. via offline xattr corruption or a concurrent path that bypasses parse_dacl()) can present num_aces = 65535 with minimal actual ACE data.  This causes a ~8 MB allocation (not kzalloc, so uninitialized) that the subsequent loop only partially populates, and may also overflow the three-way size_t multiply on 32-bit kernels.  Additionally, the ACE walk loop uses the weaker offsetof(struct smb_ace, access_req) minimum size check rather than the minimum valid on-wire ACE size, and does not reject ACEs whose declared size is below the minimum.  Reproduced on UML + KASAN + LOCKDEP against the real ksmbd code path. A legitimate mount.cifs client creates a parent directory over SMB (ksmbd writes a valid security.NTACL xattr), then the NTACL blob on the backing filesystem is rewritten to set num_aces = 0xFFFF while keeping the posix_acl_hash bytes intact so ksmbd_vfs_get_sd_xattr()'s hash check still passes.  A subsequent SMB2 CREATE of a child under that parent drives smb2_open() into smb_inherit_dacl() (share has \"vfs objects = acl_xattr\" set), which fails the page allocator:    WARNING: mm/page_alloc.c:5226 at __alloc_frozen_pages_noprof+0x46c/0x9c0   Workqueue: ksmbd-io handle_ksmbd_work    __alloc_frozen_pages_noprof+0x46c/0x9c0    ___kmalloc_large_node+0x68/0x130    __kmalloc_large_node_noprof+0x24/0x70    __kmalloc_noprof+0x4c9/0x690    smb_inherit_dacl+0x394/0x2430    smb2_open+0x595d/0xabe0    handle_ksmbd_work+0x3d3/0x1140  With the patch applied the added guard rejects the tampered value with -EINVAL before any large allocation runs, smb2_open() falls back to smb2_create_sd_buffer(), and the child is created with a default SD.  No warning, no splat.  Fix by:    1. Validating num_aces against pdacl_size using the same formula      applied in parse_dacl().    2. Replacing the raw kmalloc(sizeof * num_aces * 2) with      kmalloc_array(num_aces * 2, sizeof(...)) for overflow-safe      allocation.    3. Tightening the per-ACE loop guard to require the minimum valid      ACE size (offsetof(smb_ace, sid) + CIFS_SID_BASE_SIZE) and      rejecting under-sized ACEs, matching the hardening in      smb_check_perm_dacl() and parse_dacl().  v1 -\u003e v2:   - Replace the synthetic test-module splat in the changelog with a     real-path UML + KASAN reproduction driven through mount.cifs and     SMB2 CREATE; Namjae flagged the kcifs3_test_inherit_dacl_old name     in v1 since it does not exist in ksmbd.   - Drop the commit-hash citation from the code comment per Namjae's     review; keep the parse_dacl() pointer.",
  "id": "DEBIAN-CVE-2026-31706",
  "modified": "2026-09-14T16:47:50.410348651Z",
  "published": "2026-05-01T14:16:20.597Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://security-tracker.debian.org/tracker/CVE-2026-31706"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "upstream": [
    "CVE-2026-31706"
  ]
}