Integer underflow in Linux kernel - CVE-2026-89640

Vulnerability identifier: #VU149169

CSH Severity: Low

CVSS v4: 4.8 [CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-89640

CWE-ID: CWE-191

Exploitation vector: Local access

Exploit availability: No public exploit available

The vulnerability allows a local user to corrupt the ByteCount in a file-clone request.

The vulnerability exists due to an integer underflow in cifs_remap_file_range() when issuing a clone-to-EOF operation with a source offset beyond the end of the source file. A local user can invoke a clone-to-EOF operation with an out-of-range source offset to corrupt the ByteCount in a file-clone request.

Linux kernel
Debian Linux
Ubuntu
linux (Ubuntu package)
linux-aws (Ubuntu package)
linux-gcp (Ubuntu package)
linux-oracle (Ubuntu package)
linux-ibm (Ubuntu package)
linux-hwe-7.0 (Ubuntu package)
linux-oem-7.0 (Ubuntu package)
linux (Debian package)

Install security update from vendor's repository.

linux (Ubuntu package) - update to 7.0.0-42.42
linux-aws (Ubuntu package) - update to 7.0.0-1016.17
linux-gcp (Ubuntu package) - update to 7.0.0-1016.18
linux-oracle (Ubuntu package) - update to 7.0.0-1015.16
linux-ibm (Ubuntu package) - update to 7.0.0-1017.17
linux-hwe-7.0 (Ubuntu package) - update to 7.0.0-42.42~24.04.1
linux-oem-7.0 (Ubuntu package) - update to 7.0.0-1017.17
linux (Debian package) - update to 6.12.111-1

• https://git.kernel.org/stable/c/6c322f5cf7476ded7a9a20f7be72462065a03c68
• https://git.kernel.org/stable/c/b057ca17b656345d04669cb87f2aff9b31d873db
• https://git.kernel.org/stable/c/b098f5e5858797827666e6cd73033f52fc39b5f6
• https://git.kernel.org/stable/c/c2a0dcb5a7a1516aa6eb6d5cedca6a8e76527028

• Integer underflow in Linux kernel smb client
• Debian update for linux
• Ubuntu update for linux-oem-7.0
• Ubuntu update for linux, linux-aws, linux-gcp and more