# CVE-2026-98773: USB: cdc-acm: skip URB restart in port_shutdown if disconnected

> A use-after-free in the Linux kernel cdc-acm driver allows local attackers to execute code or cause a denial of service via USB device disconnection.

- **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:** 18 Oct 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-108779, BELL-CVE-2026-98773, DEBIAN-CVE-2026-98773, GHSA-fp39-rj9v-7xc4, UBUNTU-CVE-2026-98773

## What is CVE-2026-98773?

CVE-2026-98773 is an use after free vulnerability in Linux, published on 18 Oct 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:

USB: cdc-acm: skip URB restart in port_shutdown if disconnected

acm_port_shutdown() is called from the tty-port machinery whenever the
last user closes the port.  acm_disconnect() sets acm->disconnected and
calls tty_port_tty_vhangup(), which eventually triggers port_shutdown().
At that point acm_disconnect() has already called acm_poison_urbs() and
is about to free the control and read URBs.

However, acm_port_shutdown() unconditionally calls acm_unpoison_urbs()
and, when the ALWAYS_POLL_CTRL quirk is set, immediately re-submits the
ctrlurb and all read URBs.  If the concurrent acm_disconnect() then
frees those URBs and their DMA buffers while they are in-flight, the
result is a use-after-free in acm_ctrl_irq() or acm_read_bulk_callback()
accessing the freed DMA memory.

Fix by checking acm->disconnected after draining the delayed anchor and
returning early: if we are in a disconnect path the URBs must remain
poisoned and must not be resubmitted.

The early return is placed after the delayed-anchor drain loop because
that loop only cancels write-side accounting (wb->use = false and
autopm counter) and does not touch the hardware path.

## Which versions are affected by CVE-2026-98773?


## How do I fix CVE-2026-98773?

Apply the vendor's patch.

## Is CVE-2026-98773 being exploited?

There is no known exploitation of CVE-2026-98773 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98773 and fix it if it is affected.

What it is: CVE-2026-98773 is an use after free vulnerability in Linux, published on 18 Oct 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-2026-98773 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-2026-98773/ (Markdown: https://insights.sbomify.com/CVE-2026-98773/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98773
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98773
- OSV: https://osv.dev/vulnerability/CVE-2026-98773

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98773/
Summaries are generated and may contain mistakes; the official description above is the record.