CVE-2026-90176 ksmbd: Do not skip lock checks for single-byte ranges
Attackers can bypass byte-range locks in ksmbd to perform unauthorized reads or writes on single-byte file ranges.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-90176?
CVE-2026-90176 is a high-severity vulnerability in Linux, published on 17 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-90176?
How do I fix CVE-2026-90176?
Apply the vendor's patch.
Is CVE-2026-90176 being exploited?
There is no known exploitation of CVE-2026-90176 in the wild and no public exploit code.
Sources
Also known as AZL-102714, BELL-CVE-2026-90176, DEBIAN-CVE-2026-90176, GHSA-rxgv-prwv-26g4, UBUNTU-CVE-2026-90176.