SB20261022280 - Improper synchronization in Linux kernel smb client

Description

This security bulletin contains information about 1 vulnerability.

1) Improper synchronization (CVE-ID: CVE-2026-98684)

CWE-ID: CWE-662 - Improper Synchronization

CVSSv4: 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]

The vulnerability allows a local user to corrupt file contents on an SMB share by causing recently written data to be overwritten with zeroes.

The vulnerability exists due to improper synchronization of written data and allocated-range queries in the Linux kernel SMB client's smb3_simple_fallocate_range() function when emulating mode 0 or FALLOC_FL_KEEP_SIZE allocation for small interior ranges on Windows servers. A local user can perform writes followed by affected allocation operations on an accessible file to cause an incoherent FSCTL_QUERY_ALLOCATED_RANGES response to identify live data as unallocated holes, resulting in that data being overwritten with zeroes.

Remediation

Install update from vendor's website.

References

• https://git.kernel.org/stable/c/aa994489bd835547c191827acc460192e147032d
• https://git.kernel.org/stable/c/bf84e44ff0ed802778eafd7ecb623635379cb506
• https://git.kernel.org/stable/c/f82242fe3109a3ef72f429540b5bdde08fbfb0e4