CVE-2026-64578 (GCVE-0-2026-64578)
Vulnerability from cvelistv5
Published
2026-08-05 08:09
Modified
2026-08-19 16:29
Severity ?
8.2 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: ksmbd: validate compound request size before reading StructureSize2 When ksmbd validates a compound (chained) SMB2 request, ksmbd_smb2_check_message() reads pdu->StructureSize2 without first checking that the compound element is large enough to contain it. StructureSize2 is a 2-byte field at offset 64 (__SMB2_HEADER_STRUCTURE_SIZE) from the start of each element. The compound-walking logic only guarantees that a full 64-byte SMB2 header is present for the trailing element: when NextCommand is 0, len is reduced to the number of bytes remaining after next_smb2_rcv_hdr_off. A remote client can craft a compound request whose last element has exactly 64 bytes, so the 2-byte StructureSize2 read at offset 64 extends one byte past the receive buffer, producing a slab-out-of-bounds read. BUG: KASAN: slab-out-of-bounds in ksmbd_smb2_check_message (fs/smb/server/smb2misc.c:402) Read of size 2 at addr ffff888012ae31ac by task kworker/0:1/14 The buggy address is located 172 bytes inside of allocated 173-byte region Workqueue: ksmbd-io handle_ksmbd_work Call Trace: ... kasan_report (mm/kasan/report.c:595) ksmbd_smb2_check_message (fs/smb/server/smb2misc.c:402) handle_ksmbd_work (fs/smb/server/server.c:119) process_one_work (kernel/workqueue.c:3314) worker_thread (kernel/workqueue.c:3397) kthread (kernel/kthread.c:436) ret_from_fork (arch/x86/kernel/process.c:158) ret_from_fork_asm (arch/x86/entry/entry_64.S:245) Reject any compound element that is too small to hold StructureSize2 before dereferencing it.
References
Impacted products
Vendor Product Version
Linux Linux Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
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{
  "containers": {
    "cna": {
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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/server/smb2misc.c"
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          "product": "Linux",
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          "vendor": "Linux",
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              "version": "6.1.183",
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              "status": "unaffected",
              "version": "6.6.148",
              "versionType": "semver"
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              "status": "unaffected",
              "version": "6.12.101",
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            },
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              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.42",
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            },
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.6",
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            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
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      ],
      "cpeApplicability": [
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          "nodes": [
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                  "vulnerable": true
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              "negate": false,
              "operator": "OR"
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: validate compound request size before reading StructureSize2\n\nWhen ksmbd validates a compound (chained) SMB2 request,\nksmbd_smb2_check_message() reads pdu-\u003eStructureSize2 without first\nchecking that the compound element is large enough to contain it.\nStructureSize2 is a 2-byte field at offset 64\n(__SMB2_HEADER_STRUCTURE_SIZE) from the start of each element.\n\nThe compound-walking logic only guarantees that a full 64-byte SMB2\nheader is present for the trailing element: when NextCommand is 0, len is\nreduced to the number of bytes remaining after next_smb2_rcv_hdr_off. A\nremote client can craft a compound request whose last element has exactly\n64 bytes, so the 2-byte StructureSize2 read at offset 64 extends one byte\npast the receive buffer, producing a slab-out-of-bounds read.\n\n  BUG: KASAN: slab-out-of-bounds in ksmbd_smb2_check_message (fs/smb/server/smb2misc.c:402)\n  Read of size 2 at addr ffff888012ae31ac by task kworker/0:1/14\n  The buggy address is located 172 bytes inside of allocated 173-byte region\n  Workqueue: ksmbd-io handle_ksmbd_work\n  Call Trace:\n   ...\n   kasan_report (mm/kasan/report.c:595)\n   ksmbd_smb2_check_message (fs/smb/server/smb2misc.c:402)\n   handle_ksmbd_work (fs/smb/server/server.c:119)\n   process_one_work (kernel/workqueue.c:3314)\n   worker_thread (kernel/workqueue.c:3397)\n   kthread (kernel/kthread.c:436)\n   ret_from_fork (arch/x86/kernel/process.c:158)\n   ret_from_fork_asm (arch/x86/entry/entry_64.S:245)\n\nReject any compound element that is too small to hold StructureSize2\nbefore dereferencing it."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 8.2,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - ksmbd is an in-kernel SMB server reached over TCP/445; a remote client triggers the bug by sending a crafted compound SMB2 request that is processed in handle_ksmbd_work() \u2192 ksmbd_verify_smb_message() \u2192 ksmbd_smb2_check_message().\nAC:L - The attacker fully controls compound layout and can set the trailing element\u0027s remaining length to exactly 64 bytes so StructureSize2 is read one byte past the receive buffer; no race or attacker-uncontrollable condition is required.\nPR:N - On affected kernels before the compound SESSION_VALID check, a compound NtLmNegotiate SESSION_SETUP (pre-auth, no credentials) sets work-\u003esess and the trailing element still reaches ksmbd_smb2_check_message(); guest/anonymous SESSION_SETUP likewise needs no host privileges.\nUI:N - Exploitation requires only attacker-sent SMB2 protocol traffic to a listening ksmbd service; no victim user action is needed.\nS:U - The out-of-bounds read and any resulting kernel impact occur in the host ksmbd/workqueue context and do not cross a VM, IOMMU, or other security-authority boundary.\nC:L - The flaw is a strictly bounded slab out-of-bounds read of one byte past the receive buffer (2-byte StructureSize2 at offset 64 when only 64 bytes remain); it may disclose adjacent slab contents but not an arbitrary read primitive.\nI:N - The bug only reads past the buffer for a StructureSize2 comparison; for a 64-byte trailing element every valid command size is then rejected, and there is no out-of-bounds write or other modification primitive.\nA:H - KASAN reports a slab-out-of-bounds BUG in ksmbd_smb2_check_message(), and the same access can oops/panic hardened or redzone-enabled kernels; a remote peer can retrigger it with further crafted compound requests."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-19T16:29:02.136Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/415d0fff0451ad7ad4caa910f2bb0f562f0fd60f"
        },
        {
          "url": "https://git.kernel.org/stable/c/1b6740525f5af90868d557c31b496ae689c8c549"
        },
        {
          "url": "https://git.kernel.org/stable/c/2c307126ed8e7adddab82b8e31d962d3a2156ab1"
        },
        {
          "url": "https://git.kernel.org/stable/c/f7550a91ab211726f59cb137523b7a9eae1ac6eb"
        },
        {
          "url": "https://git.kernel.org/stable/c/f0e337e7db67cc1c832958bbb6c4026bdceacfdb"
        },
        {
          "url": "https://git.kernel.org/stable/c/ea128f06d2fb2186f0cac0c9f3e953e4d1f5c29a"
        },
        {
          "url": "https://git.kernel.org/stable/c/15b38176fd1530372905c602fde51fe89ec8c877"
        }
      ],
      "title": "ksmbd: validate compound request size before reading StructureSize2",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-64578",
    "datePublished": "2026-08-05T08:09:33.740Z",
    "dateReserved": "2026-07-19T15:36:31.798Z",
    "dateUpdated": "2026-08-19T16:29:02.136Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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