CVE-2026-89630 (GCVE-0-2026-89630)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:45 – Updated: 2026-10-19 08:50
VLAI
Title
smb: client: restore the data_offset bound in is_valid_oplock_break()
Summary
In the Linux kernel, the following vulnerability has been resolved: smb: client: restore the data_offset bound in is_valid_oplock_break() Commit 83bfbd0bb902 ("cifs: Remove the RFC1002 header from smb_hdr") changed the quantity this bound is measured against. It used to be srv->total_read minus the 4-byte RFC1002 preamble that total_read then included, so it was the SMB message length. The same commit stopped counting the preamble, and the mechanical substitution to srv->total_read - srv->pdu_size left an expression that is identically zero: standard_receive3() reads MID_HEADER_SIZE() bytes and then exactly pdu_length - MID_HEADER_SIZE() more, adding both to total_read. len is therefore 0, the subtraction below it wraps, and no __u32 DataOffset can exceed the result, so the check from commit 097f5863b1a0 ("cifs: read overflow in is_valid_oplock_break()") no longer rejects anything. Use total_read, which is now the message length on its own.
Severity
9.1 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6639 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 83bfbd0bb9025f98fa62b44f93bd67466773d1db , < 5b16a1967a01ad4496a7206a87c3eb16f1df2b05 (git)
Affected: 83bfbd0bb9025f98fa62b44f93bd67466773d1db , < ba22f575de9deeae4ae0859ca4315a7698226237 (git)
Affected: 78e718c5aa146063cd70d2cc68297c3ac41f31ee (git)
Affected: 6.18.56 , < 6.19 (semver)
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Linux Linux Affected: 6.19
Unaffected: 0 , < 6.19 (semver)
Unaffected: 7.2.4 , ≤ 7.2.* (semver)
Unaffected: 7.3 , ≤ * (original_commit_for_fix)
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{
  "containers": {
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          "product": "Linux",
          "programFiles": [
            "fs/smb/client/smb1misc.c"
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: restore the data_offset bound in is_valid_oplock_break()\n\nCommit 83bfbd0bb902 (\"cifs: Remove the RFC1002 header from smb_hdr\")\nchanged the quantity this bound is measured against.  It used to be\nsrv-\u003etotal_read minus the 4-byte RFC1002 preamble that total_read then\nincluded, so it was the SMB message length.  The same commit stopped\ncounting the preamble, and the mechanical substitution to\nsrv-\u003etotal_read - srv-\u003epdu_size left an expression that is identically\nzero: standard_receive3() reads MID_HEADER_SIZE() bytes and then exactly\npdu_length - MID_HEADER_SIZE() more, adding both to total_read.\n\nlen is therefore 0, the subtraction below it wraps, and no __u32\nDataOffset can exceed the result, so the check from commit 097f5863b1a0\n(\"cifs: read overflow in is_valid_oplock_break()\") no longer rejects\nanything.  Use total_read, which is now the message length on its own."
        }
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      "metrics": [
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            "baseSeverity": "CRITICAL",
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            "version": "3.1"
          },
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              "value": "AV:N - The flaw is in the in-kernel SMB1 client demultiplex path: a remote peer sends an unsolicited SMB_COM_NT_TRANSACT response over TCP/445 and cifs_demultiplex_thread() calls is_valid_oplock_break() on unmatched frames, so a malicious or compromised SMB server (or MITM) reaches it via network protocol data.\nAC:L - The attacker fully controls Command, Flags, ByteCount, and DataOffset in a single unsolicited frame; the broken bound wraps so any DataOffset is accepted and the resulting heap over-read is deterministic, with no race or condition the attacker cannot influence once the client is on the SMB1 connection.\nPR:N - A matching MID, session setup, or tree connect is not required: after negotiate, an unmatched NT_TRANSACT+RESPONSE frame is treated as an oplock/dnotify break before authentication, so the malicious server needs no credentials or privileges on the client host.\nUI:N - On a persistent SMB1 mount (cifsroot, automount, or an already-mounted legacy NAS share) the cifsd thread processes unsolicited frames after the existing connection or reconnect, so no additional victim action is required at attack time.\nS:U - The out-of-bounds/use-after-free read occurs in kernel heap used by the CIFS client on the same host kernel security authority and does not cross a VM, IOMMU, or sandbox boundary.\nC:H - Attacker-controlled DataOffset displaces file_notify_information into adjacent or freed cifs_small_rq slab objects (KASAN use-after-free read), and printing FileName with %s can walk unbounded kernel memory, so the disclosure is not limited to a few bounded bytes.\nI:N - The displaced pointer is only read (Action and FileName for a debug print); the bug does not write through that pointer or otherwise provide a kernel memory-modification or control-flow primitive.\nA:H - The KASAN-confirmed slab use-after-free and unmapped over-read run in the cifsd demultiplex thread and can oops or panic the kernel, and a malicious peer can repeat the unsolicited frame to retrigger the crash."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T08:50:02.437Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/5b16a1967a01ad4496a7206a87c3eb16f1df2b05"
        },
        {
          "url": "https://git.kernel.org/stable/c/ba22f575de9deeae4ae0859ca4315a7698226237"
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      "title": "smb: client: restore the data_offset bound in is_valid_oplock_break()",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89630",
    "datePublished": "2026-09-11T19:45:25.697Z",
    "dateReserved": "2026-09-11T19:38:34.738Z",
    "dateUpdated": "2026-10-19T08:50:02.437Z",
    "state": "PUBLISHED"
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        "descriptions": [
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            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: restore the data_offset bound in is_valid_oplock_break()\n\nCommit 83bfbd0bb902 (\"cifs: Remove the RFC1002 header from smb_hdr\")\nchanged the quantity this bound is measured against.  It used to be\nsrv-\u003etotal_read minus the 4-byte RFC1002 preamble that total_read then\nincluded, so it was the SMB message length.  The same commit stopped\ncounting the preamble, and the mechanical substitution to\nsrv-\u003etotal_read - srv-\u003epdu_size left an expression that is identically\nzero: standard_receive3() reads MID_HEADER_SIZE() bytes and then exactly\npdu_length - MID_HEADER_SIZE() more, adding both to total_read.\n\nlen is therefore 0, the subtraction below it wraps, and no __u32\nDataOffset can exceed the result, so the check from commit 097f5863b1a0\n(\"cifs: read overflow in is_valid_oplock_break()\") no longer rejects\nanything.  Use total_read, which is now the message length on its own."
          }
        ],
        "id": "CVE-2026-89630",
        "lastModified": "2026-10-19T09:17:59.930",
        "metrics": {
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            {
              "cvssData": {
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                "attackVector": "NETWORK",
                "availabilityImpact": "HIGH",
                "baseScore": 9.1,
                "baseSeverity": "CRITICAL",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "NONE",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H",
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              "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
              "type": "Secondary"
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        "published": "2026-09-11T20:19:48.517",
        "references": [
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          },
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        "vulnStatus": "Received"
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      "current_release_date": "2026-11-07T04:16:51+00:00",
      "cve": "CVE-2026-89630",
      "id": "CVE-2026-89630",
      "initial_release_date": "2026-09-11T00:00:00+00:00",
      "product_status:known_affected": "110",
      "product_status:known_not_affected": "93",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: smb: client: restore the data_offset bound in is_valid_oplock_break()",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89630.json",
      "version": "3"
    }
  }
}



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