CVE-2026-64391 ksmbd: use opener credentials for ADS I/O
Attackers can bypass permission checks on alternate data streams by using opener credentials, potentially reading or modifying protected files.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-64391?
CVE-2026-64391 is a critical vulnerability in Linux kernel, published on 25 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: use opener credentials for ADS I/O
Alternate data streams are stored as xattrs. Unlike regular file I/O, their read and write paths therefore call VFS xattr helpers which recheck inode permissions and LSM policy using the current task credentials.
Run ADS I/O with the credentials captured when the SMB handle was opened.
Which versions are affected by CVE-2026-64391?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-64391?
Apply the vendor's patch.
Is CVE-2026-64391 being exploited?
There is no known exploitation of CVE-2026-64391 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-64391, DEBIAN-CVE-2026-64391, GHSA-83mf-wfc5-x4x3, ROOT-OS-DEBIAN-12-CVE-2026-64391, ROOT-OS-UBUNTU-2204-CVE-2026-64391, UBUNTU-CVE-2026-64391.