# CVE-2026-72248: netfilter: flowtable: support IPIP tunnel with direct xmit

> A null pointer dereference in the Linux kernel netfilter flowtable occurs when using IPIP tunnels with direct xmit, causing a system crash.

- **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:** DEBIAN-CVE-2026-72248, GHSA-mv4h-4h45-g2xr, UBUNTU-CVE-2026-72248

## What is CVE-2026-72248?

CVE-2026-72248 is a critical 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:

netfilter: flowtable: support IPIP tunnel with direct xmit

The combination of IPIP tunnel with direct xmit, eg. bridge device,
breaks because no dst_entry is provided to check the skb headroom and to
set the iph->frag_off field. This leads to invalid dst usage and can
trigger a crash in the tunnel transmit path.

Fix this by moving dst_cache and dst_cookie out of the runtime union so
that they can be shared by neighbour, xfrm, and direct tunnel flows.
For FLOW_OFFLOAD_XMIT_DIRECT tuples carrying tunnel metadata, preserve
route state in these shared fields and release it through the common
dst release path.

Since dst_entry is now available to the three supported xmit modes and
dst_release() already deals with NULL dst, remove the xmit type check
in nft_flow_dst_release(). Moreover, skip the check if the dst entry
is NULL in nf_flow_dst_check() which is now the case for the direct
xmit case.

Based on patch from Rein Wei <n05ec@lzu.edu.cn>.

## Which versions are affected by CVE-2026-72248?


## How do I fix CVE-2026-72248?

Apply the vendor's patch.

## Is CVE-2026-72248 being exploited?

There is no known exploitation of CVE-2026-72248 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72248 and fix it if it is affected.

What it is: CVE-2026-72248 is a critical 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-2026-72248 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-2026-72248/ (Markdown: https://insights.sbomify.com/CVE-2026-72248/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72248
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72248
- OSV: https://osv.dev/vulnerability/CVE-2026-72248

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72248/
Summaries are generated and may contain mistakes; the official description above is the record.