# 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.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-101873, BELL-CVE-2026-90303, DEBIAN-CVE-2026-90303, GHSA-3rvr-4rpw-5w37, UBUNTU-CVE-2026-90303

## 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.

## Is CVE-2026-90303 being exploited?

There is no known exploitation of CVE-2026-90303 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90303 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-90303 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-90303/ (Markdown: https://insights.sbomify.com/CVE-2026-90303/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90303
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90303
- OSV: https://osv.dev/vulnerability/CVE-2026-90303

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90303/
Summaries are generated and may contain mistakes; the official description above is the record.