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CVE-2026-89640 (GCVE-0-2026-89640)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:45 – Updated: 2026-09-14 12:01
VLAI
Title
cifs: fix loff_t underflow in cifs_remap_file_range() when len == 0
Summary
In the Linux kernel, the following vulnerability has been resolved: cifs: fix loff_t underflow in cifs_remap_file_range() when len == 0 With len == 0 (clone to EOF), the effective length is computed as: len = src_inode->i_size - off; If off > i_size, this is a negative loff_t, corrupting the ByteCount in the FSCTL_DUPLICATE_EXTENTS_TO_FILE request and inverting the range in filemap_write_and_wait_range(). The existing off >= i_size check fires only after the ioctl has already been sent. Snapshot i_size_read() once for both the bounds check and the length calculation, eliminating the TOCTOU and 32-bit torn-read risk. Reject off > src_size with -EINVAL. Treat off == src_size as a no-op, consistent with __generic_remap_file_range_prep().
Severity
7.1 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 04b38d601239b4d9be641b412cf4b7456a041c67 , < f3d1ae1e6bc4a9f559185b6e7bd2b6375ec2fdd4 (git)
Affected: 04b38d601239b4d9be641b412cf4b7456a041c67 , < 7f62817fe049b0f3652518c1ba72631ec1e0a322 (git)
Affected: 04b38d601239b4d9be641b412cf4b7456a041c67 , < b098f5e5858797827666e6cd73033f52fc39b5f6 (git)
Affected: 04b38d601239b4d9be641b412cf4b7456a041c67 , < c2a0dcb5a7a1516aa6eb6d5cedca6a8e76527028 (git)
Affected: 04b38d601239b4d9be641b412cf4b7456a041c67 , < b057ca17b656345d04669cb87f2aff9b31d873db (git)
Affected: 04b38d601239b4d9be641b412cf4b7456a041c67 , < 6c322f5cf7476ded7a9a20f7be72462065a03c68 (git)
guessed Create a notification for this product.
Linux Linux Affected: 4.5
Unaffected: 0 , < 4.5 (semver)
Unaffected: 6.1.188 , ≤ 6.1.* (semver)
Unaffected: 6.6.157 , ≤ 6.6.* (semver)
Unaffected: 6.12.109 , ≤ 6.12.* (semver)
Unaffected: 6.18.50 , ≤ 6.18.* (semver)
Unaffected: 7.2.4 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc1 , ≤ * (original_commit_for_fix)
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              "versionType": "original_commit_for_fix"
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          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ncifs: fix loff_t underflow in cifs_remap_file_range() when len == 0\n\nWith len == 0 (clone to EOF), the effective length is computed as:\n\n    len = src_inode-\u003ei_size - off;\n\nIf off \u003e i_size, this is a negative loff_t, corrupting the ByteCount\nin the FSCTL_DUPLICATE_EXTENTS_TO_FILE request and inverting the range\nin filemap_write_and_wait_range().  The existing off \u003e= i_size check\nfires only after the ioctl has already been sent.\n\nSnapshot i_size_read() once for both the bounds check and the length\ncalculation, eliminating the TOCTOU and 32-bit torn-read risk.  Reject\noff \u003e src_size with -EINVAL.  Treat off == src_size as a no-op,\nconsistent with __generic_remap_file_range_prep()."
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              "value": "AV:L - The bug is in the CIFS client remap method, reached from the local FICLONERANGE/FICLONE ioctls through vfs_clone_file_range() on an already-mounted CIFS share, not from SMB packet parsing in ksmbd or the TCP stack.\nAC:L - An attacker fully controls src_offset and src_length and can set length to 0 with offset past i_size, so the loff_t underflow is deterministic and does not depend on a race or memory layout they cannot influence.\nPR:L - vfs_clone_file_range() only requires a regular source opened for read and a regular destination opened for write; any unprivileged user with those fds on a CIFS mount can issue FICLONERANGE without capabilities or init-namespace root.\nUI:N - The attacker opens their own CIFS files and issues the ioctl; no separate victim action such as mounting a share or opening a file is required once a typical enterprise/autofs CIFS mount exists.\nS:U - Impact stays inside the host kernel and the CIFS inode/page cache of the same OS security authority; this is not a VM, IOMMU, or sandbox boundary crossing.\nC:N - The underflow does not read attacker-inaccessible kernel or file data; it miscomputes a clone length and then truncates destination page cache and sends a bad FSCTL, with no out-of-bounds or UAF read primitive.\nI:H - Negative len wraps destend to a huge uoff_t so truncate_inode_pages_range() discards the destination file\u0027s page cache, including dirty folios not flushed in the inverted range, silently destroying buffered data, and the same value corrupts ByteCount in FSCTL_DUPLICATE_EXTENTS_TO_FILE.\nA:H - The same wrapped range and signed-to-u64 conversion can set a huge/negative EOF via smb2_set_file_size()/cifs_resize_file_locked() on duplicate-extents servers and leave netfs/pagecache state inconsistent, which can oops, hang, or deny access to the affected file and kernel paths."
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    "cveId": "CVE-2026-89640",
    "datePublished": "2026-09-11T19:45:33.289Z",
    "dateReserved": "2026-09-11T19:38:34.740Z",
    "dateUpdated": "2026-09-14T12:01:42.820Z",
    "state": "PUBLISHED"
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    "redhat_vex": {
      "aggregate_severity": "Low",
      "current_release_date": "2026-09-15T08:13:26+00:00",
      "cve": "CVE-2026-89640",
      "id": "CVE-2026-89640",
      "initial_release_date": "2026-09-11T00:00:00+00:00",
      "product_status:known_affected": "234",
      "product_status:known_not_affected": "42",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: cifs: fix loff_t underflow in cifs_remap_file_range() when len == 0",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89640.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "important",
      "current_release_date": "2026-09-13T16:57:41Z",
      "cve": "CVE-2026-89640",
      "id": "CVE-2026-89640",
      "initial_release_date": "2026-09-12T16:24:29Z",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-89640",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-89640.json",
      "version": "4"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.