CVE-2026-89839 f2fs: use the mount idmap for the owner check in f2fs_xattr_advise_set()
Local attackers can bypass owner checks on idmapped mounts to modify extended attributes, potentially leading to privilege escalation or unauthorized access.
- 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-2026-89839?
CVE-2026-89839 is a missing authorization vulnerability in Linux, published on 16 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:
f2fs: use the mount idmap for the owner check in f2fs_xattr_advise_set()
f2fs_xattr_advise_set() calls inode_owner_or_capable() with &nop_mnt_idmap before allowing the "system.advise" xattr to be set, instead of the idmap that the VFS passes to the ->set() handler.
f2fs supports idmapped mounts, so on such a mount this checks the caller's fsuid against the unmapped on-disk owner rather than the mapped owner: the actual owner can be wrongly denied with -EPERM and an unrelated caller wrongly allowed. Pass the handler's idmap instead.
Which versions are affected by CVE-2026-89839?
How do I fix CVE-2026-89839?
Apply the vendor's patch.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-89839 being exploited?
There is no known exploitation of CVE-2026-89839 in the wild and no public exploit code.
Sources
Also known as AZL-101223, BELL-CVE-2026-89839, DEBIAN-CVE-2026-89839, GHSA-hf9x-gfgm-hfj2, UBUNTU-CVE-2026-89839.