# CVE-2026-72124: can: isotp: serialize TX state transitions under so->rx_lock

> A race condition in the Linux kernel CAN ISO-TP driver allows concurrent access to TX state, potentially corrupting transfers and causing denial of service.

- **Severity:** High 8.8 (`CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **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:** 15 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** BELL-CVE-2026-72124, DEBIAN-CVE-2026-72124, GHSA-h95p-28wv-6wpp, UBUNTU-CVE-2026-72124

## What is CVE-2026-72124?

CVE-2026-72124 is a high-severity vulnerability in Linux, published on 15 Aug 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: serialize TX state transitions under so->rx_lock

The TX state machine (so->tx.state) is driven from three contexts:
sendmsg() claiming and progressing a transfer, the RX path consuming
Flow Control/echo frames, and two hrtimers timing out a stalled
transfer. Mixing a lock-free cmpxchg() claim in sendmsg() with
hrtimer_cancel() calls made under so->rx_lock elsewhere left windows
where a frame or timer callback could act on a state that had already
moved on, corrupting an unrelated transfer.

so->rx_lock now covers the full lifecycle of a TX claim: sendmsg()
takes it to check so->tx.state is ISOTP_IDLE, switch it to
ISOTP_SENDING, bump so->tx_gen and drain the previous transfer's
timers - all as one critical section. isotp_rcv_fc()/isotp_rcv_cf()
already run under this lock via isotp_rcv(), and isotp_rcv_echo() now
takes it itself, so none of them can ever observe a transfer mid-claim.
This also means a transfer can no longer be handed to sendmsg()'s
cleanup paths (signal or send error) while another thread is
concurrently claiming or finishing it, so those paths can cancel
timers and reset the state unconditionally.

isotp_release() claims the socket the same way, so a racing sendmsg()
sees a consistent ISOTP_SHUTDOWN and skips arming its timer or sending.

Only the hrtimer callbacks stay outside so->rx_lock, since they run
under so->rx_lock's cancellation elsewhere and taking it themselves
would deadlock. so->tx_gen lets them recognize whether the transfer
they timed out is still the one currently active, so they don't
report an error against a transfer that has since completed or been
superseded.

## Which versions are affected by CVE-2026-72124?


## How do I fix CVE-2026-72124?

Apply the vendor's patch.

## Is CVE-2026-72124 being exploited?

There is no known exploitation of CVE-2026-72124 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72124 and fix it if it is affected.

What it is: CVE-2026-72124 is a high-severity vulnerability in Linux, published on 15 Aug 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-2026-72124 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-2026-72124/ (Markdown: https://insights.sbomify.com/CVE-2026-72124/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72124
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72124
- OSV: https://osv.dev/vulnerability/CVE-2026-72124

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72124/
Summaries are generated and may contain mistakes; the official description above is the record.