# CVE-2026-72137: xfrm: nat_keepalive: avoid double free on send error

> A double free vulnerability in the Linux kernel's xfrm nat_keepalive module allows attackers to cause a denial of service or potentially execute code.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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:** 15 Aug 2026
- **Updated:** 17 Aug 2026
- **Also known as:** BELL-CVE-2026-72137, DEBIAN-CVE-2026-72137, GHSA-w74p-mj9r-98xw, UBUNTU-CVE-2026-72137

## What is CVE-2026-72137?

CVE-2026-72137 is a critical use after free vulnerability in Linux, published on 15 Aug 2026. 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:

xfrm: nat_keepalive: avoid double free on send error

nat_keepalive_send() frees the keepalive skb whenever the IPv4 or IPv6
send helper reports an error.

That cleanup is only correct before the skb is handed to the output
path. Once ip_build_and_send_pkt() or ip6_xmit() takes ownership, the
networking stack may already have consumed the skb before returning an
error, so freeing it again is unsafe.

Handle the pre-handoff failure cases inside nat_keepalive_send_ipv4()
and nat_keepalive_send_ipv6(), where the caller still owns the skb, and
keep nat_keepalive_send() responsible only for family dispatch and the
unsupported-family cleanup path.

## Which versions are affected by CVE-2026-72137?


## How do I fix CVE-2026-72137?

Apply the vendor's patch.

## Is CVE-2026-72137 being exploited?

There is no known exploitation of CVE-2026-72137 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72137 and fix it if it is affected.

What it is: CVE-2026-72137 is a critical use after free vulnerability in Linux, published on 15 Aug 2026. 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-2026-72137 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-2026-72137/ (Markdown: https://insights.sbomify.com/CVE-2026-72137/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72137
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72137
- OSV: https://osv.dev/vulnerability/CVE-2026-72137

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72137/
Summaries are generated and may contain mistakes; the official description above is the record.