# CVE-2026-80889: can: isotp: fix timer drain order, wakeup handling and tx_gen ordering

> A race condition in the Linux kernel CAN ISO-TP protocol can cause system instability or denial of service due to improper timer and state handling.

- **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:** 4 Sep 2026
- **Updated:** 4 Sep 2026
- **Also known as:** AZL-99479, BELL-CVE-2026-80889, DEBIAN-CVE-2026-80889, GHSA-r952-5653-4wq2, UBUNTU-CVE-2026-80889

## What is CVE-2026-80889?

CVE-2026-80889 is a vulnerability in Linux, published on 4 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:

can: isotp: fix timer drain order, wakeup handling and tx_gen ordering

This patch is a follow-up to commit cf070fe33bfb ("can: isotp: serialize
TX state transitions under so->rx_lock") which addresses following
sashiko-bot findings:

- isotp_sendmsg(): drain so->txfrtimer first so a stale callback can't
  re-arm echotimer after the claim

- isotp_release(): wake so->wait after forcing ISOTP_SHUTDOWN so a
  sleeping sendmsg() claim isn't stranded

- isotp_sendmsg(): have both wait_event_interruptible() calls in
  isotp_sendmsg() also wake on ISOTP_SHUTDOWN and do not return claim to
  IDLE to avoid corrupting a concurrent isotp_release() process.

- isotp_sendmsg(): handle potential claim of a new transfer when
  the wait_event_interruptible() call returns in CAN_ISOTP_WAIT_TX_DONE
  mode. Don't touch timers and states of the new transfer if a new thread
  incremented so->tx_gen before getting the lock at err_event_drop.

- isotp_sendmsg(): handle a stuck can_send() and omit timer and state
  changes if a new transfer was claimed. wait_tx_done() returns the error
  recorded in so->tx_result[], tagged with the caller's own generation.

- isotp_tx_timeout(): on a claimed timeout, record the ECOMM error for
  the timed-out transfer's own generation in so->tx_result[]; sk->sk_err
  is raised unconditionally, same as every other error path here.

- isotp_tx_gen_done()/isotp_tx_timeout(): always read tx.state (acquire)
  before tx_gen - the reverse order let a weakly ordered CPU pair a fresh
  tx.state with a stale tx_gen/tx_result slot.

- isotp_sendmsg(): wait_tx_done: drain sk_err via sock_error() once we
  have read the result from so->tx_result[], so an already-reported error
  doesn't stay latched for a later poll()/SO_ERROR.

Also align the remaining lock-free so->tx.state/rx.state/cfecho accesses
and use skb->hash as unique loopback echo frame indicator.

## Which versions are affected by CVE-2026-80889?


## How do I fix CVE-2026-80889?

Apply the vendor's patch.

## Is CVE-2026-80889 being exploited?

There is no known exploitation of CVE-2026-80889 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80889 and fix it if it is affected.

What it is: CVE-2026-80889 is a vulnerability in Linux, published on 4 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-2026-80889 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-2026-80889/ (Markdown: https://insights.sbomify.com/CVE-2026-80889/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80889
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80889
- OSV: https://osv.dev/vulnerability/CVE-2026-80889

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80889/
Summaries are generated and may contain mistakes; the official description above is the record.