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CVE-2026-89640

7.1 · HIGH

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 compu…

Published Sep 11, 2026EPSS 0.13%

Overview

CVE-2026-89640 is a high-severity vulnerability. It was published on September 11, 2026 and has a CVSS 3.1 base score of 7.1 (HIGH).

This vulnerability has a CVSS 3.1 base score of 7.1, rated HIGH. It requires local or adjacent network access to exploit. Some level of privileges is required for exploitation.

Technical 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().

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

Refgit.kernel.org/stable/c/2c6eede83b3de1268db92c7e49741761c954aa26Refgit.kernel.org/stable/c/6c322f5cf7476ded7a9a20f7be72462065a03c68Refgit.kernel.org/stable/c/7f62817fe049b0f3652518c1ba72631ec1e0a322Refgit.kernel.org/stable/c/b057ca17b656345d04669cb87f2aff9b31d873dbRefgit.kernel.org/stable/c/b098f5e5858797827666e6cd73033f52fc39b5f6Refgit.kernel.org/stable/c/c2a0dcb5a7a1516aa6eb6d5cedca6a8e76527028Refgit.kernel.org/stable/c/ce813e5eebf46851e872ce59bdc34dc5dd4e29a4Refgit.kernel.org/stable/c/f3d1ae1e6bc4a9f559185b6e7bd2b6375ec2fdd4

How CyberStrike helps

Frequently asked questions

What is CVE-2026-89640?

CVE-2026-89640 is a high-severity vulnerability. It was published on September 11, 2026 and has a CVSS 3.1 base score of 7.1 (HIGH).

How severe is CVE-2026-89640?

This vulnerability has a CVSS 3.1 base score of 7.1, rated HIGH. It requires local or adjacent network access to exploit. Some level of privileges is required for exploitation.

How do I fix or remediate CVE-2026-89640?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-89640?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-89640 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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