CVE-2026-89633 (GCVE-0-2026-89633)
Vulnerability from cvelistv5
Published
2026-09-11 19:45
Modified
2026-10-21 12:48
Severity ?
9.8 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: smb: client: fix OOB read/write from unvalidated DataOffset in coalesce_t2() coalesce_t2() computes data pointers directly from server-supplied DataOffset fields with no validation against buffer bounds: data_area_of_tgt = (char *)&pSMBt->hdr.Protocol + get_unaligned_le16(&pSMBt->t2_rsp.DataOffset); data_area_of_src = (char *)&pSMBs->hdr.Protocol + get_unaligned_le16(&pSMBs->t2_rsp.DataOffset); data_area_of_tgt += total_in_tgt; ... memcpy(data_area_of_tgt, data_area_of_src, total_in_src); A small DataOffset can push a pointer below the actual byte area, overwriting header fields; a large one can push it past the buffer end, causing out-of-bounds heap reads (source) or writes (target). The BCC overflow guard does not prevent this: BCC reflects how much data is present, while DataOffset controls where in the buffer it starts. The "validate target area" comment present since the function was first written in 2005 was a placeholder that was never implemented. Add lower- and upper-bound checks for both data pointers before the memcpy, and before any target header fields are modified.
References
Impacted products
Vendor Product Version
Linux Linux Version: e4eb295d38b57f4d4b956942a48887eb252d97c6
Version: e4eb295d38b57f4d4b956942a48887eb252d97c6
Version: e4eb295d38b57f4d4b956942a48887eb252d97c6
Version: e4eb295d38b57f4d4b956942a48887eb252d97c6
Version: e4eb295d38b57f4d4b956942a48887eb252d97c6
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{
  "containers": {
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      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/client/smb1transport.c"
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          "vendor": "Linux",
          "versions": [
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              "version": "2.6.12"
            },
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              "status": "unaffected",
              "version": "0",
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              "status": "unaffected",
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              "status": "unaffected",
              "version": "6.12.113",
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              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.51",
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              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.4",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
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        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.6.160",
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                  "vulnerable": true
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                  "vulnerable": true
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              "operator": "OR"
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: fix OOB read/write from unvalidated DataOffset in coalesce_t2()\n\ncoalesce_t2() computes data pointers directly from server-supplied\nDataOffset fields with no validation against buffer bounds:\n\n  data_area_of_tgt = (char *)\u0026pSMBt-\u003ehdr.Protocol +\n                     get_unaligned_le16(\u0026pSMBt-\u003et2_rsp.DataOffset);\n  data_area_of_src = (char *)\u0026pSMBs-\u003ehdr.Protocol +\n                     get_unaligned_le16(\u0026pSMBs-\u003et2_rsp.DataOffset);\n  data_area_of_tgt += total_in_tgt;\n  ...\n  memcpy(data_area_of_tgt, data_area_of_src, total_in_src);\n\nA small DataOffset can push a pointer below the actual byte area,\noverwriting header fields; a large one can push it past the buffer\nend, causing out-of-bounds heap reads (source) or writes (target).\nThe BCC overflow guard does not prevent this: BCC reflects how much\ndata is present, while DataOffset controls where in the buffer it\nstarts.\n\nThe \"validate target area\" comment present since the function was\nfirst written in 2005 was a placeholder that was never implemented.\n\nAdd lower- and upper-bound checks for both data pointers before the\nmemcpy, and before any target header fields are modified."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 9.8,
            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - coalesce_t2() runs in cifs_demultiplex_thread on SMB1 TRANS2 responses received over TCP/445; a malicious or compromised SMB1 server (or MITM on an unsigned session) delivers the crafted DataOffset/DataCount fields entirely over the network.\nAC:L - The server fully controls DataOffset, DataCount, and TotalDataCount in both primary and secondary TRANS2 PDUs and can force a large first fragment so mid-\u003eresp_buf is set; the unbounded memcpy is deterministic with no race or condition outside the attacker\u2019s control.\nPR:N - The attacker is the remote SMB peer and needs no account or privileges on the victim; coalesce_t2() runs in the demux thread before validate_t2() or any local capability check, and session credentials belong to the client mount, not the attacking server.\nUI:N - Once an SMB1 CIFS mount exists (fstab, autofs, embedded/industrial NAS; CONFIG_CIFS_ALLOW_INSECURE_LEGACY defaults on), reconnect and ordinary lookup/readdir/getattr plus cifs_qfs_tcon QUERY_FS_INFO issue TRANS2 automatically, so the server can trigger coalescing with no further user action.\nS:U - The out-of-bounds heap read/write corrupts the client kernel\u2019s own cifs_request slab within the same host security authority; this is not a VM escape, IOMMU bypass, or sandbox boundary crossing.\nC:H - An unvalidated source DataOffset lets memcpy read far past the secondary response (DataOffset is a 16-bit value up to 65535 versus a ~16KB cifs_request object), disclosing adjacent kernel heap; the same memory-corruption primitive can be leveraged for further disclosure.\nI:H - An unvalidated target DataOffset lets memcpy write attacker-controlled bytes past the primary buffer (or backward into the SMB header); the BCC-size guard does not constrain where the copy starts, yielding an out-of-bounds write exploitable for control-flow hijacking.\nA:H - Reading or writing tens of kilobytes past the cifs_request allocation can fault on unmapped pages and oops or panic the demux thread, and a malicious server can retrigger it on every multi-part TRANS2."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-21T12:48:05.616Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/6eb70b78e48b0031bd1a05fe1b58959a48e87739"
        },
        {
          "url": "https://git.kernel.org/stable/c/36d01415d881d5326a0dd3384f781cd7e69aff2d"
        },
        {
          "url": "https://git.kernel.org/stable/c/672cf86aa6aa0fb4012ce4c3b3498df42ad67a4e"
        },
        {
          "url": "https://git.kernel.org/stable/c/033bc80019f07d158630df4e69b19a49010f54f1"
        },
        {
          "url": "https://git.kernel.org/stable/c/6343c1da561962688f203362d80d6a3bfa39fa1b"
        }
      ],
      "title": "smb: client: fix OOB read/write from unvalidated DataOffset in coalesce_t2()",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89633",
    "datePublished": "2026-09-11T19:45:28.083Z",
    "dateReserved": "2026-09-11T19:38:34.739Z",
    "dateUpdated": "2026-10-21T12:48:05.616Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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