CVE-2026-90176: ksmbd: Do not skip lock checks for single-byte ranges

Severity: high (CVSS 8.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-17 · updated 2026-10-19

Description

In the Linux kernel, the following vulnerability has been resolved: ksmbd: Do not skip lock checks for single-byte ranges check_lock_range() uses inclusive ranges. Its callers pass the end offset as start + length - 1, so start == end represents a valid single-byte range rather than an empty range. The start == end shortcut therefore skips mandatory byte-range lock checks for one-byte reads, writes, copychunk operations and one-byte truncate ranges. A conflicting lock covering that byte is not checked and the operation is allowed to proceed. Remove the shortcut. The truncate size == inode->i_size case is already handled by only calling check_lock_range() when the new size differs from the current file size.

Affected products

Linux kernel: from 6.1.160 before 6.1.188; from 6.6.120 before 6.6.157; from 6.12.64 before 6.12.110; from 6.18.3 before 6.18.52; 6.19 — fixed in 6.1.188, 6.12.110, 6.18.52, 6.6.157, 7.3

How to fix

Upgrade to a fixed version: Linux kernel 6.1.188, 6.12.110, 6.18.52, 6.6.157. Check the vendor advisory for mitigations.

References

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