# CVE-2025-40183: bpf: Fix metadata_dst leak __bpf_redirect_neigh_v{4,6}

> A memory leak in the Linux kernel's BPF redirect helper can exhaust kernel memory, leading to denial of service.

- **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:** 12 Nov 2025
- **Updated:** 15 Oct 2026
- **Also known as:** BELL-CVE-2025-40183, DEBIAN-CVE-2025-40183, GHSA-553v-hjpm-738q, ROOT-OS-UBUNTU-2404-CVE-2025-40183, UBUNTU-CVE-2025-40183

## What is CVE-2025-40183?

CVE-2025-40183 is a high-severity denial of service vulnerability in Linux, published on 12 Nov 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:

bpf: Fix metadata_dst leak __bpf_redirect_neigh_v{4,6}

Cilium has a BPF egress gateway feature which forces outgoing K8s Pod
traffic to pass through dedicated egress gateways which then SNAT the
traffic in order to interact with stable IPs outside the cluster.

The traffic is directed to the gateway via vxlan tunnel in collect md
mode. A recent BPF change utilized the bpf_redirect_neigh() helper to
forward packets after the arrival and decap on vxlan, which turned out
over time that the kmalloc-256 slab usage in kernel was ever-increasing.

The issue was that vxlan allocates the metadata_dst object and attaches
it through a fake dst entry to the skb. The latter was never released
though given bpf_redirect_neigh() was merely setting the new dst entry
via skb_dst_set() without dropping an existing one first.

## Which versions are affected by CVE-2025-40183?


## How do I fix CVE-2025-40183?

Apply the vendor's patch.

## Is CVE-2025-40183 being exploited?

There is no known exploitation of CVE-2025-40183 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40183 and fix it if it is affected.

What it is: CVE-2025-40183 is a high-severity denial of service vulnerability in Linux, published on 12 Nov 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-2025-40183 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-2025-40183/ (Markdown: https://insights.sbomify.com/CVE-2025-40183/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40183
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40183
- OSV: https://osv.dev/vulnerability/CVE-2025-40183

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40183/
Summaries are generated and may contain mistakes; the official description above is the record.