Description
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().
Published: 2026-09-11
Score: 6.3 Medium
EPSS: < 1% Very Low
KEV: No
Impact: Data corruption and possible denial of service through CIFS file range remapping
Action: Patch
AI Analysis

Impact

A negative loff_t occurs in the CIFS server’s remap function when a remap request with zero length and an offset beyond the source file size is processed. The integer underflow can lead to an out‑of‑bounds write (CWE-787), corrupting the ByteCount field of the FSCTL_DUPLICATE_EXTENTS_TO_FILE request. The miscalculation can invert the write range handled by the kernel, potentially leading to filesystem corruption or a crash of the CIFS service.

Affected Systems

All Linux kernel versions that implement the CIFS server prior to the inclusion of the bound check introduced by the referenced commit SHA.

Risk and Exploitability

The flaw is exploitable by a CIFS client that can issue the FSCTL_DUPLICATE_EXTENTS_TO_FILE ioctl over SMB. The attacker can trigger the underflow by specifying an offset greater than the source file size, which may cause denial of service or.3, the vulnerability is considered medium severity. The EPSS score is <1%, indicating a low likelihood of exploitation, and the vulnerability is not listed in the CISA KEV catalog. The systems that expose CIFS services.

Generated by OpenCVE AI on September 13, 2026 at 01:06 UTC.

Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

  • Upgrade the Linux kernel to a version referencing the commit SHA in the advisory.
  • If an immediate kernel upgrade is firewall rules or disabling the CIFS server if it is not required.
  • Monitor system logs for occurrence of the FSCTL_DUPLICATE_EXTENTS_TO_FILE ioctl and other anomalous kernel messages that may indicate exploitation attempts.

Generated by OpenCVE AI on September 13, 2026 at 01:06 UTC.

Tracking

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Advisories

No advisories yet.

History

Sat, 12 Sep 2026 16:45:00 +0000

Type Values Removed Values Added
Weaknesses CWE-190

Sat, 12 Sep 2026 12:15:00 +0000

Type Values Removed Values Added
Weaknesses CWE-787
References
Metrics threat_severity

None

 cvssV3_1

{'score': 6.3, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H'}

threat_severity

Important

Sat, 12 Sep 2026 09:30:00 +0000

Type Values Removed Values Added
Weaknesses CWE-190

Fri, 11 Sep 2026 23:45:00 +0000

Type Values Removed Values Added
Description 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().
Title cifs: fix loff_t underflow in cifs_remap_file_range() when len == 0
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References

Subscriptions

Linux Linux Kernel
cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-09-11T19:45:33.289Z

Reserved: 2026-09-11T19:38:34.740Z

Link: CVE-2026-89640

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-09-11T20:19:49.733

Modified: 2026-09-11T20:19:49.733

Link: CVE-2026-89640

cve-icon Redhat

Severity : Important

Publid Date: 2026-09-11T19:45:33Z

Links: CVE-2026-89640 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-09-13T01:15:14Z

Weaknesses