CVE-2026-90263 btrfs: check if root is readonly when setting posix acl
Attackers can modify POSIX ACLs on read-only Btrfs filesystems, bypassing intended write restrictions and altering file permissions.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-90263?
CVE-2026-90263 is a vulnerability in Linux, published on 17 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
btrfs: check if root is readonly when setting posix acl
For a filesystem which has btrfs read-only property set to true, all write operations including acl and xattr should be denied. However, acl can still be set even if btrfs ro property is true.
This happens because no function on the set_acl code path checks the root is readonly or not. It was checked in btrfs_setxattr_trans() but got removed in commit 353c2ea735e4 ("btrfs: remove redundant readonly root check in btrfs_setxattr_trans")
That commit didn't check if all the callers properly check the root's read-only flag. A previous fix is commit b51111271b03 ("btrfs: check if root is readonly while setting security xattr").
Always check if the root is read-only before performing the set acl operation.
Which versions are affected by CVE-2026-90263?
How do I fix CVE-2026-90263?
Apply the vendor's patch.
Is CVE-2026-90263 being exploited?
There is no known exploitation of CVE-2026-90263 in the wild and no public exploit code.
Sources
Also known as AZL-102465, BELL-CVE-2026-90263, DEBIAN-CVE-2026-90263, GHSA-wxw8-hpqh-3xg2, UBUNTU-CVE-2026-90263.