# CVE-2026-90140: cuse: wait for pending RCU callbacks on module exit

> A use-after-free in the Linux kernel CUSE module allows local attackers to execute arbitrary code or cause a denial of service by unloading the module while RCU callbacks are pending.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **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-102567, BELL-CVE-2026-90140, DEBIAN-CVE-2026-90140, GHSA-h4xp-2gp9-vpwg, UBUNTU-CVE-2026-90140

## What is CVE-2026-90140?

CVE-2026-90140 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:

cuse: wait for pending RCU callbacks on module exit

Since commit 053fc4f755ad ("fuse: fix UAF in rcu pathwalks"),
fuse_conn_put() frees the fuse_conn through call_rcu() rather than
synchronously.  For cuse, fc->release is cuse_fc_release(), which
lives in the cuse module.  If the module is removed before the RCU
grace period ends, the callback jumps into freed module memory:

      userspace / module unload      |        RCU softirq
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 close(/dev/cuse)                    |
  cuse_channel_release()             |
   fuse_dev_release()                |
    fuse_conn_put(fch->conn)         |
     call_rcu(delayed_release) ------+---> callback queued
                                     |
 rmmod cuse                          |
  cuse_exit()                        |
   cuse_channel_destroy()            |
   ...                               |
   return                            |
                                     |
 <module text freed>                 |
                                     |  rcu_do_batch()
                                     |   delayed_release()
                                     |    fc->release()
                                     |     -> cuse_fc_release()
                                     |        ^^^ freed text!

The freed module text is unmapped by vfree(), so the jump into the
stale callback triggers a page-fault Oops.  If the virtual address
is subsequently reused, the callback could execute unrelated code
(undefined behaviour).

Fix this by calling rcu_barrier() in cuse_exit() so that any pending
fuse_conn release callback completes before the module is removed.

## Which versions are affected by CVE-2026-90140?


## How do I fix CVE-2026-90140?

Apply the vendor's patch.

## Is CVE-2026-90140 being exploited?

There is no known exploitation of CVE-2026-90140 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90140 and fix it if it is affected.

What it is: CVE-2026-90140 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-2026-90140 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-2026-90140/ (Markdown: https://insights.sbomify.com/CVE-2026-90140/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90140
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90140
- OSV: https://osv.dev/vulnerability/CVE-2026-90140

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90140/
Summaries are generated and may contain mistakes; the official description above is the record.