# CVE-2020-36789: can: dev: can_get_echo_skb(): prevent call to kfree_skb() in hard IRQ context

> A NULL pointer dereference in the Linux kernel CAN stack can cause a system crash when processing network congestion in hardware IRQ context.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 17 Apr 2025
- **Updated:** 11 May 2026
- **Also known as:** DEBIAN-CVE-2020-36789, GHSA-5974-c6r6-2pv9, UBUNTU-CVE-2020-36789

## What is CVE-2020-36789?

CVE-2020-36789 is a medium-severity vulnerability in Linux kernel, published on 17 Apr 2025. 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: dev: can_get_echo_skb(): prevent call to kfree_skb() in hard IRQ context

If a driver calls can_get_echo_skb() during a hardware IRQ (which is often, but
not always, the case), the 'WARN_ON(in_irq)' in
net/core/skbuff.c#skb_release_head_state() might be triggered, under network
congestion circumstances, together with the potential risk of a NULL pointer
dereference.

The root cause of this issue is the call to kfree_skb() instead of
dev_kfree_skb_irq() in net/core/dev.c#enqueue_to_backlog().

This patch prevents the skb to be freed within the call to netif_rx() by
incrementing its reference count with skb_get(). The skb is finally freed by
one of the in-irq-context safe functions: dev_consume_skb_any() or
dev_kfree_skb_any(). The "any" version is used because some drivers might call
can_get_echo_skb() in a normal context.

The reason for this issue to occur is that initially, in the core network
stack, loopback skb were not supposed to be received in hardware IRQ context.
The CAN stack is an exeption.

This bug was previously reported back in 2017 in [1] but the proposed patch
never got accepted.

While [1] directly modifies net/core/dev.c, we try to propose here a
smoother modification local to CAN network stack (the assumption
behind is that only CAN devices are affected by this issue).

[1] http://lore.kernel.org/r/57a3ffb6-3309-3ad5-5a34-e93c3fe3614d@cetitec.com

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2020-36789?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2020-36789?

Apply the vendor's patch.

## Is CVE-2020-36789 being exploited?

There is no known exploitation of CVE-2020-36789 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-36789 and fix it if it is affected.

What it is: CVE-2020-36789 is a medium-severity vulnerability in Linux kernel, published on 17 Apr 2025. 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-2020-36789 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2020-36789/ (Markdown: https://insights.sbomify.com/CVE-2020-36789/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-36789
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-36789
- OSV: https://osv.dev/vulnerability/CVE-2020-36789

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-36789/
Summaries are generated and may contain mistakes; the official description above is the record.