# CVE-2025-68241: ipv4: route: Prevent rt_bind_exception() from rebinding stale fnhe

> A race condition in the Linux kernel IPv4 routing code can cause a device reference count leak, leading to denial of service when unregistering network devices.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 16 Dec 2025
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2025-68241, DEBIAN-CVE-2025-68241, GHSA-vwj6-rppm-qjrp, ROOT-OS-DEBIAN-12-CVE-2025-68241, ROOT-OS-DEBIAN-13-CVE-2025-68241, ROOT-OS-UBUNTU-2204-CVE-2025-68241, ROOT-OS-UBUNTU-2404-CVE-2025-68241, UBUNTU-CVE-2025-68241

## What is CVE-2025-68241?

CVE-2025-68241 is a high-severity vulnerability in Linux, published on 16 Dec 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

ipv4: route: Prevent rt_bind_exception() from rebinding stale fnhe

The sit driver's packet transmission path calls: sit_tunnel_xmit() ->
update_or_create_fnhe(), which lead to fnhe_remove_oldest() being called
to delete entries exceeding FNHE_RECLAIM_DEPTH+random.

The race window is between fnhe_remove_oldest() selecting fnheX for
deletion and the subsequent kfree_rcu(). During this time, the
concurrent path's __mkroute_output() -> find_exception() can fetch the
soon-to-be-deleted fnheX, and rt_bind_exception() then binds it with a
new dst using a dst_hold(). When the original fnheX is freed via RCU,
the dst reference remains permanently leaked.

CPU 0                             CPU 1
__mkroute_output()
  find_exception() [fnheX]
                                  update_or_create_fnhe()
                                    fnhe_remove_oldest() [fnheX]
  rt_bind_exception() [bind dst]
                                  RCU callback [fnheX freed, dst leak]

This issue manifests as a device reference count leak and a warning in
dmesg when unregistering the net device:

  unregister_netdevice: waiting for sitX to become free. Usage count = N

Ido Schimmel provided the simple test validation method [1].

The fix clears 'oldest->fnhe_daddr' before calling fnhe_flush_routes().
Since rt_bind_exception() checks this field, setting it to zero prevents
the stale fnhe from being reused and bound to a new dst just before it
is freed.

[1]
ip netns add ns1
ip -n ns1 link set dev lo up
ip -n ns1 address add 192.0.2.1/32 dev lo
ip -n ns1 link add name dummy1 up type dummy
ip -n ns1 route add 192.0.2.2/32 dev dummy1
ip -n ns1 link add name gretap1 up arp off type gretap \
    local 192.0.2.1 remote 192.0.2.2
ip -n ns1 route add 198.51.0.0/16 dev gretap1
taskset -c 0 ip netns exec ns1 mausezahn gretap1 \
    -A 198.51.100.1 -B 198.51.0.0/16 -t udp -p 1000 -c 0 -q &
taskset -c 2 ip netns exec ns1 mausezahn gretap1 \
    -A 198.51.100.1 -B 198.51.0.0/16 -t udp -p 1000 -c 0 -q &
sleep 10
ip netns pids ns1 | xargs kill
ip netns del ns1

## Which versions are affected by CVE-2025-68241?


## How do I fix CVE-2025-68241?

Apply the vendor's patch.

## Is CVE-2025-68241 being exploited?

There is no known exploitation of CVE-2025-68241 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-68241 and fix it if it is affected.

What it is: CVE-2025-68241 is a high-severity vulnerability in Linux, published on 16 Dec 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-68241 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-2025-68241/ (Markdown: https://insights.sbomify.com/CVE-2025-68241/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-68241
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-68241
- OSV: https://osv.dev/vulnerability/CVE-2025-68241

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-68241/
Summaries are generated and may contain mistakes; the official description above is the record.