CVE-2026-89632 (GCVE-0-2026-89632)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:45 – Updated: 2026-10-21 12:48
VLAI
Title
smb: client: fix use-before-check of ReparseDataLength in reparse_buf_ptr()
Summary
In the Linux kernel, the following vulnerability has been resolved: smb: client: fix use-before-check of ReparseDataLength in reparse_buf_ptr() reparse_buf_ptr() reads buf->ReparseDataLength before checking that count covers the full fixed header: buf = (struct reparse_data_buffer *)((u8 *)io + off); len = sizeof(*buf); /* 8 bytes */ rdlen = le16_to_cpu(buf->ReparseDataLength); /* offset 4, 2 bytes */ if (count < len || count < rdlen + len) /* check comes after */ struct reparse_data_buffer has ReparseDataLength at offset 4. If a server returns OutputCount < 6, the read at offset 4-5 reaches past the end of the received data. The off+count bounds against iov_len were already validated, but that does not protect against count being smaller than sizeof(*buf). Split the check: verify count >= sizeof(*buf) before reading ReparseDataLength, then verify count covers the data region.
Severity
8.2 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
SSVC
Exploitation: none Automatable: yes Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-16 19:24 UTC
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6971 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: a158bb66b1373866d9fd5997565a58a573085539 , < b70bc592afd19732e2e4563300ebe8f974280365 (git)
Affected: 67ec9949b0dfe78c99e110dd975eb7dc5645630c , < 711cf71300d7992f450600df8864917d3538679f (git)
Affected: 67ec9949b0dfe78c99e110dd975eb7dc5645630c , < 05f78e6cf34ea3a285053bd5999e08e8ac298bd5 (git)
Affected: 6.6.32 , < 6.6.160 (semver)
guessed Create a notification for this product.
Linux Linux Affected: 6.8
Unaffected: 0 , < 6.8 (semver)
Unaffected: 6.6.160 , ≤ 6.6.* (semver)
Unaffected: 7.2.4 , ≤ 7.2.* (semver)
Unaffected: 7.3 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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              "lang": "en",
              "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: fix use-before-check of ReparseDataLength in reparse_buf_ptr()\n\nreparse_buf_ptr() reads buf-\u003eReparseDataLength before checking that\ncount covers the full fixed header:\n\n    buf = (struct reparse_data_buffer *)((u8 *)io + off);\n    len = sizeof(*buf);                          /* 8 bytes */\n    rdlen = le16_to_cpu(buf-\u003eReparseDataLength); /* offset 4, 2 bytes */\n\n    if (count \u003c len || count \u003c rdlen + len)      /* check comes after */\n\nstruct reparse_data_buffer has ReparseDataLength at offset 4.  If a\nserver returns OutputCount \u003c 6, the read at offset 4-5 reaches past\nthe end of the received data.  The off+count bounds against iov_len\nwere already validated, but that does not protect against count being\nsmaller than sizeof(*buf).\n\nSplit the check: verify count \u003e= sizeof(*buf) before reading\nReparseDataLength, then verify count covers the data region."
            }
          ],
          "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 - The flaw is in the in-kernel SMB client parser for FSCTL_GET_REPARSE_POINT IOCTL replies on TCP/445. A malicious, compromised, or on-path SMB server reaches reparse_buf_ptr() with crafted OutputOffset/OutputCount; this matches sibling client response-parsing scores such as CVE-2026-46155 and CVE-2024-49996.\nAC:L - The server fully controls OutputOffset and OutputCount. A successful IOCTL PDU with OutputCount \u003c 6 and OutputOffset near iov_len (for example a 448-byte cifs_small_rq-sized frame) deterministically loads ReparseDataLength past the received payload, with no race or attacker-uncontrollable layout.\nPR:N - The attacker is the remote SMB server (or a MITM on an unsigned session) and needs no account, credentials, or capabilities on the victim client. GET_REPARSE runs on an already established tree connect after ordinary CREATE/lookup; the client authenticates to the server, not the reverse.\nUI:N - On an already-mounted or automounted CIFS share, any routine lookup/stat of a reparse point \u2014 including files the server flags as reparse in CREATE \u2014 issues FSCTL_GET_REPARSE_POINT. Backup jobs, indexers, and inode revalidation hit the parser with no contemporaneous victim mount action.\nS:U - The two-byte out-of-bounds load and any resulting oops stay inside the client kernel\u0027s security authority. The bug does not cross a VM, IOMMU, or sandbox boundary.\nC:L - The use-before-check reads exactly two bytes of ReparseDataLength past the IOCTL output region (and, when the PDU fills cifs_small_rq, past that 448-byte slab). Those bytes are passed only to smb_EIO2 tracing, so disclosure is strictly bounded, matching CVE-2026-64448 rather than unbounded heap leaks.\nI:N - The out-of-bounds access is a u16 load used only in the subsequent length check and error trace. On failure the helper returns -EIO and does not install a reparse tag or copy payload, so there is no kernel write or metadata-corruption primitive.\nA:H - A PDU that fills the cifs_small_rq or cifs_request slab with OutputOffset at the object end makes the two-byte load a true slab-out-of-bounds access, which KASAN reports as a BUG and which can oops/panic if the next page is unmapped. A malicious server can retrigger it on every GET_REPARSE."
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-10-21T12:48:04.460Z",
            "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "shortName": "Linux"
          },
          "references": [
            {
              "url": "https://git.kernel.org/stable/c/b70bc592afd19732e2e4563300ebe8f974280365"
            },
            {
              "url": "https://git.kernel.org/stable/c/711cf71300d7992f450600df8864917d3538679f"
            },
            {
              "url": "https://git.kernel.org/stable/c/05f78e6cf34ea3a285053bd5999e08e8ac298bd5"
            }
          ],
          "title": "smb: client: fix use-before-check of ReparseDataLength in reparse_buf_ptr()",
          "x_generator": {
            "engine": "bippy-1.2.0"
          }
        }
      },
      "cveMetadata": {
        "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "assignerShortName": "Linux",
        "cveId": "CVE-2026-89632",
        "datePublished": "2026-09-11T19:45:27.325Z",
        "dateReserved": "2026-09-11T19:38:34.738Z",
        "dateUpdated": "2026-10-21T12:48:04.460Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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