# CVE-2026-74543: net: udp_tunnel: fix memory leak in udp_tunnel_nic_unregister()

> A memory leak in the Linux kernel UDP tunnel NIC offload code allows local attackers to exhaust system memory, causing denial of service.

- **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:** 15 Aug 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-96258, BELL-CVE-2026-74543, DEBIAN-CVE-2026-74543, GHSA-6fp2-p6pg-3j24, UBUNTU-CVE-2026-74543

## What is CVE-2026-74543?

CVE-2026-74543 is a memory corruption 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:

net: udp_tunnel: fix memory leak in udp_tunnel_nic_unregister()

syzbot reported a memory leak [1] in the UDP tunnel NIC offload code.

When device registration fails (e.g. in register_netdevice()), netdev core
unwinds by sending a single NETDEV_UNREGISTER notification. If work was queued
during NETDEV_REGISTER (utn->work_pending is set), udp_tunnel_nic_unregister()
returns early:

	if (utn->work_pending)
		return;

Because failed registrations do not enter netdev_wait_allrefs_any(), no
subsequent NETDEV_UNREGISTER rebroadcast will ever occur. As a result, the
struct udp_tunnel_nic allocated in udp_tunnel_nic_alloc() is leaked
permanently.

Fix this by removing the early return. Instead, synchronously cancel any
pending work with cancel_delayed_work_sync() before freeing @utn.

To be able to call cancel_delayed_work_sync() while holding RTNL (the work also
needs RTNL), switch udp_tunnel_nic_device_sync_work() to rtnl_trylock(). If RTNL
is contended, requeue the work with a 1 jiffy delay (via queue_delayed_work())
to prevent high CPU contention while waiting for RTNL lock.

The utn->work_pending bookkeeping is no longer needed and is removed, as
the workqueue core already tracks the pending/running state of the work.

[1]
BUG: memory leak
unreferenced object 0xffff888127d5f840 (size 96):
  comm "syz-executor", pid 5806, jiffies 4294942188
  backtrace (crc 99fdb6c8):
    __kmalloc_noprof+0x3bf/0x550
    udp_tunnel_nic_alloc net/ipv4/udp_tunnel_nic.c:756 [inline]
    udp_tunnel_nic_register net/ipv4/udp_tunnel_nic.c:833 [inline]
    udp_tunnel_nic_netdevice_event+0x804/0xab0 net/ipv4/udp_tunnel_nic.c:931
    notifier_call_chain+0x59/0x160 kernel/notifier.c:85
    call_netdevice_notifiers_info+0x7d/0xb0 net/core/dev.c:2250
    register_netdevice+0xc10/0xeb0 net/core/dev.c:11478

## Which versions are affected by CVE-2026-74543?


## How do I fix CVE-2026-74543?

Apply the vendor's patch.

## Is CVE-2026-74543 being exploited?

There is no known exploitation of CVE-2026-74543 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74543 and fix it if it is affected.

What it is: CVE-2026-74543 is a memory corruption 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-2026-74543 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-2026-74543/ (Markdown: https://insights.sbomify.com/CVE-2026-74543/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74543
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74543
- OSV: https://osv.dev/vulnerability/CVE-2026-74543

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74543/
Summaries are generated and may contain mistakes; the official description above is the record.