CVE-2026-90303 ARM: 9485/1: mm: acquire mmap write lock around show_pte() for user faults
A race condition in the Linux kernel ARM memory management can cause a use-after-free and kernel panic when debug user faults are enabled.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-90303?
CVE-2026-90303 is an use after free 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:
ARM: 9485/1: mm: acquire mmap write lock around show_pte() for user faults
When CONFIG_DEBUG_USER=y, and cmdline "user_debug=31" is set, a user fault may trigger show_pte() without any lock. If another thread in the same process concurrently calls munmap(), the page table pages may be freed while show_pte() is still traversing them, causing a use-after-free in show_pte().
If CONFIG_ARM_LPAE=y, this may cause a kernel panic if the pages table of PMD are freed when show_pte() is running.
Acquire mmap_write_lock() around show_pte() for user faults to fix the contention.
For user faults, additionally restrict that show_pte() is called only when the addr is a user-space address (addr < TASK_SIZE). This is because the lock of tsk->mm only protects the virtual memory of user address space, furthermore, dumping the page tables of a kernel-space address for user faults is unnecessary and may have security implications.
Keep everything unchanged for kernel faults, because the kernel is already in the "oops" state, acquiring a lock may risk a deadlock.
Which versions are affected by CVE-2026-90303?
How do I fix CVE-2026-90303?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-90303 being exploited?
There is no known exploitation of CVE-2026-90303 in the wild and no public exploit code.
Sources
Also known as AZL-101873, BELL-CVE-2026-90303, DEBIAN-CVE-2026-90303, GHSA-3rvr-4rpw-5w37, UBUNTU-CVE-2026-90303.