# CVE-2026-98368: esp: downgrade zerocopy managed frags before mutating skb frags

> A use-after-free vulnerability in the Linux kernel's ESP implementation allows attackers to execute code or cause denial of service via crafted network packets.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-106310, BELL-CVE-2026-98368, DEBIAN-CVE-2026-98368, GHSA-jw2q-x793-gp2m, UBUNTU-CVE-2026-98368

## What is CVE-2026-98368?

CVE-2026-98368 is a high-severity use after free vulnerability in Linux, published on 6 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

esp: downgrade zerocopy managed frags before mutating skb frags

On the out-of-place output path (esp->inplace == false) ESP rewrites the
skb frag array: esp_output_head() appends a trailer frag and
esp_output_tail() replaces the frags with a destination page, both
referenced with get_page().

When the skb carries zerocopy managed frags (SKBFL_MANAGED_FRAG_REFS) the
payload frags are owned by the ubuf and must not be referenced or
unreferenced individually, but ESP mutates the frag array without ever
downgrading the skb.  This breaks the managed-frag invariant two ways:

  - esp_ssg_unref() walks the source scatterlist and drops a page
    reference for every frag, including the ubuf-owned payload frags,
    pushing their refcount below the GUP pin bias while the pages are
    still pinned, i.e. a use-after-free of the zerocopy pages;

  - esp_output_tail() installs its destination page as frag 0 with
    get_page() but leaves SKBFL_MANAGED_FRAG_REFS set, so
    skb_release_data() takes the skip_unref branch and never drops that
    reference, leaking the x->xfrag page at packet rate.

Fix this the way every other frag-mutating site does (__ip_append_data(),
__ip6_append_data(), tcp_sendmsg_locked()) and call
skb_zcopy_downgrade_managed() before ESP touches the frag array: it takes
a real reference on each existing frag and clears SKBFL_MANAGED_FRAG_REFS,
so the per-frag unref in esp_ssg_unref() and the frag release in
skb_release_data() are both balanced and no mixed-ownership frag array is
left behind.

## Which versions are affected by CVE-2026-98368?


## How do I fix CVE-2026-98368?

Apply the vendor's patch.

## Is CVE-2026-98368 being exploited?

There is no known exploitation of CVE-2026-98368 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98368 and fix it if it is affected.

What it is: CVE-2026-98368 is a high-severity use after free vulnerability in Linux, published on 6 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-98368 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-2026-98368/ (Markdown: https://insights.sbomify.com/CVE-2026-98368/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98368
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98368
- OSV: https://osv.dev/vulnerability/CVE-2026-98368

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98368/
Summaries are generated and may contain mistakes; the official description above is the record.