# CVE-2026-72126: can: isotp: use unconditional synchronize_rcu() in isotp_release()

> A race condition in the Linux kernel CAN ISO-TP module allows a use-after-free of a timer callback, potentially leading to code execution or system crash.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **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-2026-72126, DEBIAN-CVE-2026-72126, GHSA-5j9g-r9x8-9248, UBUNTU-CVE-2026-72126

## What is CVE-2026-72126?

CVE-2026-72126 is a high-severity use after free 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: use unconditional synchronize_rcu() in isotp_release()

isotp_notify() unregisters the (RCU) CAN filters via can_rx_unregister()
and clears so->bound without waiting for a grace period. isotp_release()
uses so->bound to decide whether it needs to call synchronize_rcu()
before cancelling so->rxtimer, so when NETDEV_UNREGISTER runs first it
skips that synchronize_rcu() and can cancel the timer while an
in-flight isotp_rcv() is still executing and about to re-arm it via
isotp_send_fc(), leading to a use-after-free timer callback on the
freed socket.

sakisho-bot remarked a problem with rtnl_lock held in isotp_notify(),
therefore make isotp_release() always call synchronize_rcu() before
cancelling the timers, regardless of so->bound. This still closes the
original race (isotp_notify() clearing so->bound without waiting for
in-flight isotp_rcv() callers before isotp_release() cancels the RX
timer) without adding any RCU wait to the netdevice notifier path.

## Which versions are affected by CVE-2026-72126?


## How do I fix CVE-2026-72126?

Apply the vendor's patch.

## Is CVE-2026-72126 being exploited?

There is no known exploitation of CVE-2026-72126 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72126 and fix it if it is affected.

What it is: CVE-2026-72126 is a high-severity use after free 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-2026-72126 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-2026-72126/ (Markdown: https://insights.sbomify.com/CVE-2026-72126/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72126
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72126
- OSV: https://osv.dev/vulnerability/CVE-2026-72126

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72126/
Summaries are generated and may contain mistakes; the official description above is the record.