CVE-2026-90231 apparmor: fix unconfined user namespace restriction forced stack
A flaw in AppArmor allows unconfined user namespace restrictions to be bypassed, enabling privilege escalation via stacked transitions.
- 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-2026-90231?
CVE-2026-90231 is a high-severity 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:
apparmor: fix unconfined user namespace restriction forced stack
If a task is already confined by a stack the unprivileged transition restriction on unconfined is not correctly, applied. This results in an escape if two transitions through an unconfined profile can be executed.
Fix this by pushing the check into the per profile label build. The check will always be done against unconfined and result in a stack of just the unconfined component when necessary.
Which versions are affected by CVE-2026-90231?
How do I fix CVE-2026-90231?
Apply the vendor's patch.
Is CVE-2026-90231 being exploited?
There is no known exploitation of CVE-2026-90231 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-90231, DEBIAN-CVE-2026-90231, GHSA-24pv-j52f-w4hj, UBUNTU-CVE-2026-90231.