# CVE-2026-64566: xfrm: iptfs: propagate SKBFL_SHARED_FRAG in iptfs_skb_add_frags()

> A missing flag propagation in the Linux kernel's IPTFS module allows memory corruption and potential code execution during ESP decryption.

- **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:** 5 Aug 2026
- **Updated:** 17 Aug 2026
- **Also known as:** BELL-CVE-2026-64566, DEBIAN-CVE-2026-64566, GHSA-wr7x-h83j-8fqg, UBUNTU-CVE-2026-64566

## What is CVE-2026-64566?

CVE-2026-64566 is a critical memory corruption vulnerability in Linux, published on 5 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: iptfs: propagate SKBFL_SHARED_FRAG in iptfs_skb_add_frags()

When iptfs_skb_add_frags() copies frag references from the source
frag walk into a new SKB, it increments the page reference count via
__skb_frag_ref() but does not propagate SKBFL_SHARED_FRAG to the
destination SKB's skb_shinfo->flags.

If the source SKB carries shared frags (e.g. from a page-pool backed
receive path), the new inner SKB will appear to ESP as having privately
owned frags.  A subsequent esp_input() call for a nested transport-mode
SA then takes the no-COW fast path and decrypts in place, writing over
pages that are still referenced by the outer IPTFS SKB.  This causes
kernel-visible memory corruption and can trigger a panic.

All other frag-transfer helpers in the kernel (skb_try_coalesce,
skb_gro_receive, __pskb_copy_fclone, skb_shift, skb_segment) correctly
propagate SKBFL_SHARED_FRAG; align iptfs_skb_add_frags() with this
convention by setting the flag inside the loop immediately after
__skb_frag_ref() and nr_frags++, so every exit path that attaches a frag
unconditionally propagates SKBFL_SHARED_FRAG.

## Which versions are affected by CVE-2026-64566?


## How do I fix CVE-2026-64566?

Apply the vendor's patch.

## Is CVE-2026-64566 being exploited?

There is no known exploitation of CVE-2026-64566 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-64566 and fix it if it is affected.

What it is: CVE-2026-64566 is a critical memory corruption vulnerability in Linux, published on 5 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-2026-64566 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-2026-64566/ (Markdown: https://insights.sbomify.com/CVE-2026-64566/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64566
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64566
- OSV: https://osv.dev/vulnerability/CVE-2026-64566

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64566/
Summaries are generated and may contain mistakes; the official description above is the record.