{
  "affected": [
    {
      "ranges": [
        {
          "events": [
            {
              "introduced": "e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9"
            },
            {
              "fixed": "282cbbb476b9f35793452bc461934af4c7eca169"
            },
            {
              "fixed": "f20adc4ef7428bc485ee83fd1a592252fb87718b"
            },
            {
              "fixed": "325d4ac11f526cb8964cff14548ccf02d8c756d8"
            },
            {
              "fixed": "95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c"
            },
            {
              "fixed": "90089584b2e25c4510b7b987387b4405f0673ece"
            },
            {
              "fixed": "151b1799861fde38087c08f613abc2843ef597b0"
            },
            {
              "fixed": "d07b26f39246a82399661936dd0c853983cfade7"
            }
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "type": "GIT"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Linux",
        "name": "Kernel"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "5.15.0"
            },
            {
              "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": "6.12.84"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "6.13.0"
            },
            {
              "fixed": "6.18.25"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "6.19.0"
            },
            {
              "fixed": "7.0.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "cna_assigner": "Linux",
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31712.json"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: require minimum ACE size in smb_check_perm_dacl()\n\nBoth ACE-walk loops in smb_check_perm_dacl() only guard against an\nunder-sized remaining buffer, not against an ACE whose declared\n`ace-\u003esize` is smaller than the struct it claims to describe:\n\n  if (offsetof(struct smb_ace, access_req) \u003e aces_size)\n      break;\n  ace_size = le16_to_cpu(ace-\u003esize);\n  if (ace_size \u003e aces_size)\n      break;\n\nThe first check only requires the 4-byte ACE header to be in bounds;\nit does not require access_req (4 bytes at offset 4) to be readable.\nAn attacker who has set a crafted DACL on a file they own can declare\nace-\u003esize == 4 with aces_size == 4, pass both checks, and then\n\n  granted |= le32_to_cpu(ace-\u003eaccess_req);               /* upper loop */\n  compare_sids(\u0026sid, \u0026ace-\u003esid);                         /* lower loop */\n\nreads access_req at offset 4 (OOB by up to 4 bytes) and ace-\u003esid at\noffset 8 (OOB by up to CIFS_SID_BASE_SIZE + SID_MAX_SUB_AUTHORITIES\n* 4 bytes).\n\nTighten both loops to require\n\n  ace_size \u003e= offsetof(struct smb_ace, sid) + CIFS_SID_BASE_SIZE\n\nwhich is the smallest valid on-wire ACE layout (4-byte header +\n4-byte access_req + 8-byte sid base with zero sub-auths).  Also\nreject ACEs whose sid.num_subauth exceeds SID_MAX_SUB_AUTHORITIES\nbefore letting compare_sids() dereference sub_auth[] entries.\n\nparse_sec_desc() already enforces an equivalent check (lines 441-448);\nsmb_check_perm_dacl() simply grew weaker validation over time.\n\nReachability: authenticated SMB client with permission to set an ACL\non a file.  On a subsequent CREATE against that file, the kernel\nwalks the stored DACL via smb_check_perm_dacl() and triggers the\nOOB read.  Not pre-auth, and the OOB read is not reflected to the\nattacker, but KASAN reports and kernel state corruption are\npossible.",
  "id": "CVE-2026-31712",
  "modified": "2026-07-15T01:49:04.177708120Z",
  "published": "2026-05-01T13:56:08.583Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/151b1799861fde38087c08f613abc2843ef597b0"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/282cbbb476b9f35793452bc461934af4c7eca169"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/325d4ac11f526cb8964cff14548ccf02d8c756d8"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/90089584b2e25c4510b7b987387b4405f0673ece"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/d07b26f39246a82399661936dd0c853983cfade7"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f20adc4ef7428bc485ee83fd1a592252fb87718b"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31712.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-31712"
    },
    {
      "type": "PACKAGE",
      "url": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
    }
  ],
  "schema_version": "1.8.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "ksmbd: require minimum ACE size in smb_check_perm_dacl()"
}