# CVE-2026-23209: macvlan: fix error recovery in macvlan_common_newlink()

> A use-after-free in the Linux kernel macvlan driver allows local attackers to crash the system or potentially execute code via crafted network link configurations.

- **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:** 14 Feb 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-77739, BELL-CVE-2026-23209, CLSA-2026-1784274653, DEBIAN-CVE-2026-23209, GHSA-89j4-f3cq-gm32, ROOT-OS-DEBIAN-11-CVE-2026-23209, ROOT-OS-DEBIAN-12-CVE-2026-23209, ROOT-OS-DEBIAN-13-CVE-2026-23209, ROOT-OS-UBUNTU-2204-CVE-2026-23209, ROOT-OS-UBUNTU-2404-CVE-2026-23209, SUSE-SU-2026:1231-1, UBUNTU-CVE-2026-23209

## What is CVE-2026-23209?

CVE-2026-23209 is a high-severity use after free vulnerability in Linux kernel, published on 14 Feb 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:

macvlan: fix error recovery in macvlan_common_newlink()

valis provided a nice repro to crash the kernel:

ip link add p1 type veth peer p2
ip link set address 00:00:00:00:00:20 dev p1
ip link set up dev p1
ip link set up dev p2

ip link add mv0 link p2 type macvlan mode source
ip link add invalid% link p2 type macvlan mode source macaddr add 00:00:00:00:00:20

ping -c1 -I p1 1.2.3.4

He also gave a very detailed analysis:

<quote valis>

The issue is triggered when a new macvlan link is created  with
MACVLAN_MODE_SOURCE mode and MACVLAN_MACADDR_ADD (or
MACVLAN_MACADDR_SET) parameter, lower device already has a macvlan
port and register_netdevice() called from macvlan_common_newlink()
fails (e.g. because of the invalid link name).

In this case macvlan_hash_add_source is called from
macvlan_change_sources() / macvlan_common_newlink():

This adds a reference to vlan to the port's vlan_source_hash using
macvlan_source_entry.

vlan is a pointer to the priv data of the link that is being created.

When register_netdevice() fails, the error is returned from
macvlan_newlink() to rtnl_newlink_create():

        if (ops->newlink)
                err = ops->newlink(dev, &params, extack);
        else
                err = register_netdevice(dev);
        if (err < 0) {
                free_netdev(dev);
                goto out;
        }

and free_netdev() is called, causing a kvfree() on the struct
net_device that is still referenced in the source entry attached to
the lower device's macvlan port.

Now all packets sent on the macvlan port with a matching source mac
address will trigger a use-after-free in macvlan_forward_source().

</quote valis>

With all that, my fix is to make sure we call macvlan_flush_sources()
regardless of @create value whenever "goto destroy_macvlan_port;"
path is taken.

Many thanks to valis for following up on this issue.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-23209?

It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `kernel-livepatch-SLE15-SP4_Update_48` | SUSE:Linux Enterprise Live Patching 15 SP4 | All versions | 2-150400.2.1 |

Products: Linux kernel.

## How do I fix CVE-2026-23209?

Apply the vendor's patch.

## Is CVE-2026-23209 being exploited?

There is no known exploitation of CVE-2026-23209 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-2026-23209 and fix it if it is affected.

What it is: CVE-2026-23209 is a high-severity use after free vulnerability in Linux kernel, published on 14 Feb 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-2026-23209 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-2026-23209/ (Markdown: https://insights.sbomify.com/CVE-2026-23209/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23209
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23209
- OSV: https://osv.dev/vulnerability/CVE-2026-23209

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-23209/
Summaries are generated and may contain mistakes; the official description above is the record.